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Home , Crop (anatomy), Gross Anatomy, Insect morphology, Lepismatidae, Proventriculus, Silverfish

THE INTERNAL OF THE OTENCLEPISMA CAMPBELLI BARNHART AND SACCHARINA LINNAEUS (: )

DISSERTATION Presented in Pertial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University

By CLYDE STERLING BARNHART, SR., B.Sc., M.Sc

The Ohio State University 1958

Approved byj

Department PREFACE

In 19^7 the writer began a study of the - tion of a silverfish collected from the Main Library on the Ohio State University campus. This began under the direction of the late Dr. C. H. Kennedy, professor of , the Ohio State University, in his course on anatomy. Professor Kennedy was Impressed with the minute detail with which the tracheation could be traced since this insect was so small. It was his interest and encouragement which prompted the writer to continue this work beyond the course and later to expand it into the more complete study embodied in this dissertation. The writer is grateful to the late professor Kennedy for his part in providing the original encouragement for this study. The writer wishes also to express his sincere gratitude to Dr. Donald J. Borror, professor of Entomo­ logy* The Ohio State University, for his helpful guidance and suggestions in bringing the work of this dissertation to completion.

li TABLE CP CONTENTS Pege INTRODUCTION...... 1 MATERIALS AND METHODS...... 2 TIES ...... 4 THE ALIMENTARY CANAL...... 14 THE CENTRAL ...... 24 THE DORSAL VESSEL...... 28 THE REPRODUCTIVE ORGANS...... 32 ABBREVIATIONS USED ON FIGURES...... 40 FIGURES...... 43 SUMMARY...... 65 BIBLIOGRAPHY...... 68

ill LIST OF ILLUSTRATIONS

Figure Page 1 Tracheation of the head, , and first abdominal segment of C . campbelll...... 44 2 Tracheation of the of C. campbelll...... 46 3 of the alimentary canal of £L*. campbelll...... 43 4 Gross anatomy of the alimentary canal of the L,. saccharlna...... 48 5 Histological longitudinal section of the wall of the in C. campbelll ...... 48

6 Histological longitudinal section of the wall of the crop in L. saccharina...... 48 7 Histological cross section of the crop wall in C^. campbelll...... 43 8 Histological cross section of the crop wall in L*. saccharlna...... 48 9 Histological cross section of the proventricular wall in C. camnbell 1...... 50 10 Histological cross section of the proventricular wall in L. saccharlna...... 50 11 Histological cross section of the wall of the mesenteron of C . Campbell!...... 50 12 Histological cross section of the wall of the mesenteron of L. saccharlna...... 50

lv 13 Histological cross section of the wall of the of campbelll.... 50 14 Histological cross section of the wall of the rectum of saccharlna... 50

15 Histological cross section of a malpighian tubule in C,*. campbelll.... 50

16 Histological cross section of a malpighian tubule in L*. saccharlna.... 50 17' Histological longitudinal section of the rectal gland of Cj_ campbelll..... 50 18 Histological longitudinal section of the rectal gland of L*. saccharlna.... 50 19 Histological section of lobe of Cj_ campbelll...... 52

20 Histological section of salivary gland lobe of campbelll...... 52

21 Histological section of salivary gland lobe of saccharlna...... 52

22 Gross anatomy of the central nervous system in campbelll...... 54

23 Gross anatomy of the central nervous system in saccharlna...... 54 24 Gross anatomy of the dorsal vessel in C. campbelll...... 56

25 Gross anatomy of the dorsal vessel in h x . saccharlna...... 56 26 Histological cross section of the dorsal vessel in £*. campbelll...... 56 2? Histological cross section of the dorsal vessel in L*. saccharlna...... 56 v 28 Ostium in open position (A) in closed position (B) in the dorsal vessel of campbelli. (dipgramme tic)..... 29 Gross anatomy of pericerdipl cells of the dorsal vessel of saccherine in segments 2 end 3 ......

30 Hlstologicpl section near the posterior tip of the dorsal vessel in C . campbelli...... 31 Histological section of the posterior tip of the dorsal vessel in C . campbelli...... 32 Histological penultimate serial section of the posterior terminus of the dorspl vessel of L_. saccharine...... 33 Gross anatomy of the reproductive organs of the female C_. cempbelli...... 34 Gross anatomy of the reproductive organs of the female ssccharina .... 35 Histological sagittal section of the posterior of the abdomen of the female C. campbelll...... 36 Histological sagittal section of the posterior of the abdomen of the female L. saccharlna...... 37 Gross anatomy of the reproductive organs of the male C_. campbelli...... 38 Gross anatomy of the reproductive organs of the male L_. saccharlna ...... 39 Histological longitudinal section of a testis of cempbelli...... 40 Histological longitudinal section of a testis of L. saccharine......

vi Figure Page 41 Histological section of the tip of the ovariole of £*. campbelll...... 62 42 Histological section of the tip of the ovariole of Xu. saccharlna ...... 62 43 Histological section of the apical group in the testis of Q j_ campbelll 62 44 Histological cross section of a seminal vesicle of J2*. campbelll...... 62 45 Histological cross section of a seminal vesicle of Xu. saccharlna...... 62

k 6 Histological cross section of glandular reproductive tube in the male L. saccharlna...... 62 47 Histological cross section of a vas efferens of campbelll...... 62 48 Histological cross section of a vas efferens of Xu. saccharlna...... 62 49 Histological cross section of a vas deferens of campbelll ...... 62 50 Histological cross section of a vas deferens of Xu. saccharlna...... 62 51 Histological cross section of a glandular reproductive tube in the male campbelll...... 62 52 Histological cross section of a glandular reproductive tube in the male L. saccharlna...... 62

53 CL_ oamplaeUJLi A, B, Histological cross sections of the aedeagus. C, Histological cross section of the body wall at base of the aedeagus. Dy Histological cross section of the glandular reproductive tubes just beneath the body wall from base of the aedeagus...... 64 vii Figure Page

5 h L. saccharlna: A, Histological cross section of the aedeagus. 3, C, Histological cross sections through the body wall at base of the aedeagus D, Histological cross sections of the glandular reproductive tubes just beneath the body wall at the base of the aedeagus..6^

viil INTRODUCTION

Sllverfish are primitive in that they are wingless (having no evidence of ever having had wings in their ancestry) and have styli which are rudiments of abdominal appendages. These are of special interest to workers on the phylogeny of the class as they furnish probable evidence as to the nature of the ancestor of pterygote insects. Snodgrass (1935» P. 212) describes a hypothetical immediate ancestor of the as having the body differentiated into head, thorax, and abdomen, with a series of three partly overlapping paranotal lobes pro­ jecting on each side of the body from the thoracic terga. Except for paranotal extensions, sllverfish fit the description of Snodgrass' hypothetical pterygote ancestor. Lepismatidae are considered by many to be the most advanced of the (Little, 195?)* Furthermore present forms are considered to have departed little from the condition of the forms preceding winged Insects (Crampton, 1916, p. 12). This study has for its purpose the exploration of the internal anatomy of two related Lepismatidae to further clarify their position in insect phylogeny. MATERIALS AND METHODS

The two species of sllverfish used for this study were wild-caught, the supply being replenished as needed. Ctenoleplsma campbelll Barnhart was obtained readily by the simple expedient of placing a pinch of oatmeal beneath a board on the concrete floor in a corner of the room where they occur. The sllverfish congregated beneath this board and were collected periodically. Lepl.sma saccharlna Linnaeus were caught by sifting through the floor litter in protected corners of two barns. As many as twenty were taken from a hollow piece of corn-stalk. A separate laboratory culture jar, with oatmeal, a plugged vial of water, and some shelter, was provided for each species. An individual selected for was anesthe­ tized with and half embedded, by use of a heated needle, in a wax dissecting dish by melting the wax around the insect body. A binocular dissecting microscope with three objec­ tives (IX, 3X, 6X) and three oculars (9X, 12X, 15X) was used with as bright illumination as could be had without melting the dissecting dish wax. Glycerine was used as the dissecting fluid for tracheae and normal saline was used for the other organs. Tissues were differentiated by periodic flooding with a mixture of neutral red and methylene blue in saline. Excess stain and debris was washed away as necessary. Small scalpels, prepared by slivering thin razor blades (Kennedy, 1932, p. 78), were very useful in dissection operations. The gross anatomy of both species was drawn from dissection of live material. For histological preparations, whole insects were fixed in boiling xvater (ten seconds) and Carnoy’s (one hour), several punctures being made along the body. They were infiltrated with 50°C - 52°C paraffin and embedded in 60°C - 62°C paraffin. All sections were of whole insects at ten microns. Staining with iron hematoxylin and eosin was effected by the use of the buffered alcohol technique of Craig and Wilson (1937). Histological sections were examined under a compound microscope using a 10X eyepiece, 1.8 mm, 4 mm and 16 mm, oculars. The details in all drawings of sections were those seen with the 1.8 mm oil immersion objective. Drawings were made with the aid of a camera lucida, the details being filled in freehand. THE RESPIRATORY SYSTEM (Figures 1-2)

Lehman (1925) has shown that the basic pattern of the tracheal system in insects has ten pairs of inter­ connected spiracles — a pair on the meso- and meta­ thorax and the first eight abdominal segments. This arrangement (according to Lehman) is normal for Thysanura (Lepismatidae), , Plecoptera, , and Isoptera, and may occur elsewhere as in (ApisT ). Lehman has also shown that the tracheal system begins in the insect embryo as a series of spiracu- lar pits segmentally arranged. Kennedy (1922) discusses the development of the tracheal branches from these pits and demonstrates the homologies of these branches through­ out the insect. Grassi (1887) shows that the tracheal system in an insect more primitive than Lepismatidae (Thysanura: Machllls) is a series of disconnected seg­ mental systems. The tracheal systems in higher insects display varied modifications.of the basic pattern of Lehman, such as reduction in the number of spiracles (Clmex) (Weber, 1933» p. ^36), development of specialized structures as air-sacs (Musca) (Packard, 1898, p. ^57)» and air-tubes () (Snodgrass, 1935* P» ^37)• The respiratory systems in both sllverfish, C. campbelll and L,. saccharlna. correspond remarkably to the basic tracheal pattern (Lehman, 1925) for insects, each having a pair of spiracles situated well forward on the , a pair on the and a pair on each of the first eight abdominal segments. Sulc (1°27, Fig. 2) has drawn the tracheal system of Leplsma saccharlna in excellent detail. His drawing is referred to when making comparison to the tracheal system of L*_ saccharlna.

The nomenclature of the tracheal system of Ctenole- plsma campbelli (Figures 1, 2) follows Kennedy (1922). Head (Figure 1). In both species the head (H) is tracheated by two cephalic dorsal branches (CD3) and two cephalic ventral branches (CVB) continuing from the dor­ sal and ventral forks of the prothoraclc tracheal trunks (PT) arising from the spiracular pits (SP) of the raeso- thoracic spiracles (S). Each cephalic dorsal branch (CDB) rebranches on reaching the head; one branch (FT) proceeds towards the mid-dorsal areas of the head; the other branch (AL) again divides, one division (A) extending into the , the other division (L) to the labrum.

In £ jl. campbelll. the cephalic ventral branch (CVB) bifur­ cates upon reaching the head, one fork (OM) branching to the eye (OB) and to the mandible (MB). The other fork 6 proceeds ventrad, turns sharply towards the center and anastomoses with its partner to form the cephalic ventral commissure (CVC). From each end of this commissure is a branch to the (MX) and one to the maxillary palpus (MP). The cephalic ventral branch (CVB) (upon reaching the head, and prior to bifurcating) gives off a branch (LP) to the labial palpus. Ijj. saccharlna differs in that a branch (not found in campbelll) leads to the eye from the corresponding trachea (AL) of Figure 1, and that the labial palpus is tracheated by a branch from the cephalic ventral commissure (Sulc, 1927). (Figure 1, P). This segment is tracheated by branches from the two prothoracic tracheal trunks (PT), each of which extends forward from the corresponding spiracular pit (SP) on either side of the mesothorax (MS). Each prothoracic tracheal trunk immediately on reaching the prothorax, gives off a small branch (PV) to the viscera

(in £jl camnbelll only). The prothoracic tracheal trunk divides near the center of the segment, forming the cephalic dorsal branch (CDB) and the cephalic ventral branch (CVB). Each cephalic dorsal branch extends a limb (PL) into its respective paranotum, then leads forward into the head. The cephalic ventral branch (CVB) gives rise to a short forked branch near the center of the pro­ thorax. One fork (LT) leads to the prothoracic leg and 7

the other joins its partner forming the prothoracic ventral commissure (PVC). Branching from each end of this commissure (PVC) a trachea (FM) leads to the femoral muscle of each prothoracic leg. Mesothorax (Figure 1, MS). This segment is served by its own spiracles (S) and one branch (an assymmetric connective-AC) from the metathorax. The mesotherscic ventral commissure (MVC) is joined, ..at its exact center, by the branch (AC) from either the right or the left raetathorecic spiracular pit (SP)'L. A spiracular trunk (ST) rises dorsally from this pit and has two branches, the anterior dorsal connective (ADC) end the posterior dorsal connective (PDC). The anterior dorsal connective apparently leads to the dorsal vessel. The posterior dorsal connective joins -with the anterior corsal connec­ tive of the metethorex forming an intersegments 1 dorssl arch (DA).

The writer has found that in campbelli the ratio of right handed to left handed assymmetry is about one to one in both . Gressi (1887, Figure 23) shows this same assymmetry in the more primitive Thysanuran Nicole tee. Sulc (1927), shows this same assymmetry in L. saccharine Wu (1923, p. 29 and Figures 98, y9 and 100) shows a pfciy- morphism occurring in the mesothorex in 3 out of 78 Nemours (Plecoptere). Instead of a usual ventral com* missural cross, the traches formed in its place either two independent ventral commissures or two independent lon­ gitudinal ventral connectives. 8

Leading ventrad and caudad from each spiracular pit is a branch (VB) which branches first to the mesothoracic leg (LT), then to the mesothoracic femoral leg muscle (PM), theh, by anatomosis with its partner, forms the ventral mesothoracic commissure (MVC). Metathorax (Figure 1 MT). The spiracles of this segment (S) open into relatively short spiracular pits (SP). Three tracheae arise from each pit, the spiracular trunk (ST), the metathoracic ventral branch (MVB) and the visceral branch (MV). The spiracular trunk divides into the anterior (ADC) and posterior (PDC) dorsal connectives, which unite with the corresponding connectives of neigh­ boring segments to form each intersegmental dorsal arch (DA). The metathoracic ventral branch (MVB) branches first to the leg (LT), then to femoral muscle (PM), then joins its partner to form the metathoracic ventral commissure (MTVC). Each visceral branch (MV^, MV2), assymmetric in this segment, proceeds ventrad from its respective spiracu­ lar pit (SP). The smaller branch (MV1) blfurestes, each fork (VF) leading to the viscera. The larger brbnch (MV2) divides, one fork (AC) uniting with the center of the mesothoracic ventral commissure (MVC), and the other fork (LVP) extending caudad into abdominal segment one (1). In It,, saccharlna fork LVF is comparatively short (Sulc,

1927). 9

Abdomen (Figure 2). Both cempbelli end L. aaooherins heve e peir of spiracles on each of abdominel segments one to eight (1-8). Each splrecie (S) leads into a spiracular pit (SP) from which srise two branches. One of these branches (AV) extends ventrad, meeting its partner to form the abdominal ventral commissure (VC) of each segment. In Cj^ campbelli no ganglionic tracheae were found arising from the ventral commissure (VC) of segment I. In segments 2 - 4 there are two close sseym- metric ganglionic tracheal branches (G,G), one extending cephalad along the midventre 1 line into the next body segment and the other extending caudad only a short distance within its own segment. In segments o - 7, ganglionic tracheal branches (G,G) consist of a sym­ metric pair, spaced apart end extending caudad; those branches are longer in segment 5 than in segments 6 and 7, and extend into segment 7. In saccharine each ventral commissure has four small branches near its center, two cephalad and two caudad, leading to abdominal ganglia 1-7.

In C_2_ campbelll each ventral branch (AVI) ks it extends ventrad, gives off a branch (STY) homologous with the leg tracheae (LT) of the thorax. These are probably remnants of stylal tracheae. They ere present in L. 10 saccharlna (Sulc, 1927) but have apparently become di­ verted to the paratergites in segments 2 - 7 even though they consistently branch from the ventral commissures.

Snodgrass (1931, P. *0 says "No positive evidence can be adduced from the known facts of anatomy or embry­ ology to establish the homology either of the stylus or the gonopophysis. Many structural interrelationships however suggest that the stylus is the telopodite of the appendage and that the gonopophysis is an endite process of the basis." Comstock (1925, P* *0 says that styli are vestigial legs in Thysanura. In Machllls (Thysanura) a pair of abdominal styli occur on each of segments 2 - 9 (Comstock, 1925, Figure 90). In L. saccharlna. a pair of styli occur on segments 8 and 9. In campbelll they occur only on segment 9, but the tracheae of vestigial styli on segments 1 - 8 are apparently retained (Figure 2, STY). In campbelll the tracheal branches to the maxillary palpi (Figure 1, MP), the legs (Figure 1, LT), the vestigial styli of segments 1 - 8 (Figure 2, STY), the styli of segment 9 (Figure 2, STY), and the gono- pophyses of segments 8 and 9 (Figure 2, OE, ON), all appear to be similarly branched from their respective ventral commissures (Figures 1, 2, VC), indicating the probable homology of these appendages. This is in accord with the embryologlcal findings of Wheeler (1893)» 11

The visceral tracheae (VT) in £*. campbelll arise from the spiracular pits (SP) in segments 3-6, but are ves­ tigial or absent in segments 1, 2, and 7. The visceral tracheae ,in L*.saccharlna. occur in segments 1 - 7 similarly stemming from the spiracular pits; these are conspicuously larger in abdominal segment 3.

The spiracular trunks (ST) in Q j_ campbelll stem directly from the spiracular pits in segments 1, 2 and 7 only; they occur as branches of visceral tracheae(VT) in segments 3-6. The visceral tracheae in L. saccharlna stem regularly from their corresponding spiracular pits in segments 1-7. In both species each spiracular trunk (ST) extends dorsad and bifurcates in the usual manner into the anterior (ADC) and posterior (PDC) dorsal connectives forming (by anatomosls) their respective dorsal arches (DA) with their counterparts of neighboring segments. In campbelll segment 8 bears the last pair of spiracles. Each in this segment leads into a very short spiracular pit (SPg); two branches leading from this pit supply segments 3 - 12^. A ventral branch (AVg) extends ventrad and anastomoses with its partner to form the ventral commissure (VC). Two branches (G, G) extend cephalad from near the middle of the ventral com­ missure to abdominal ganglia 7, 8 (Figure 22). Branching

^Heymons (1897) has demonstrated embryologically that in saccharlna segment 10 has been combined with segment 11, bearing the cerci and the terminal filament. Segment 12 is represented by the supra-anal and sub-anal lamina. 12 caudad near the center of the ventral commissure 8 are two pairs of tracheae, the Inner pair leading to the gonopophyses arising from segment 8 C3E), the outer pair branching inward to the 'gonopophyses arising from segment 9 (ON) then extending Into the styli of that segment. Each spiracular trunk (STg) extends dorsad from the spiracular pit and divides into the anterior (ADC) and the posterior (PDC) dorsal connectives. The anterior dorsal connective unites with the posterior dorsal con­ nective (PDC) of segment 7, forming the lntersegmental dorsal arch (DA) on either side. Each posterior dorsal connective (PDC) bifurcates in segment 9. The inner fork gives off two visceral tracheae (VT), then extends (TF) into the terminal filament. The outer fork branches to the anal lamina (AL) of segment 12, then extends (CR) into the . L. saccharlna differs from campbelll in the tracheation of segments 8-12 (Sulc, 1927). There is no ventral commissure in segment 8, the ventral branches leading only to either side of ganglion 8; the gonopophyses and styli of segments 8 and 9, cercl and terminal filament of segments 9-11, and anal lamina of segment 12 are sup­ plied by branches of a single pair of tracheae extending caudad from the spiracular pits of segment 8; the spira­ cular trunk extending dorsad from each spiracular pit has no posterior dorsal connective; and, in segment 8, branches extend inward from each spiracular pit, a visceral branch (not found in campbelll) and one which Sulc (1927) labels wtr paratergalls,w THE ALIMENTARY CANAL (Figures 3-21)

The alimentary canal of L*. saccharlna has been described by Grassi (138?, Figure 33). Since his work does not include a detailed , L*. saccharlna is

Included with Q camobelll in this study. The writer follows the terminology of Snodgrass (1935> Chapter XIII) applied to the parts of the alimentary canal. The alimentary canal in both species (Figures 3> *0 can be said to be generalized in that it is a relatively straight tube extending from the buccal cavity to the , and is little longer than the body. The alimentary canal is readily differentiated into stomodeum (ST 0), mesen­ teron (MENT), and proctodeum (PR), having salivary glands (SG), (PVT), gastric caeca (GC), malpighian tubules (MPT), and rectal gland (EG) all well developed. The Stomodeum. The stomodeum extends from the to the cardiac at the junction of the proventriculus and mesenteron and Includes the buccal cavity, , oesophagus, crop, proventriculus, and cardiac valve. Both species have mouth parts equipped for the Ingestion of solid food. The buccal cavity, pharynx, and the forward end of the oesophagus are in the head.

14 15

The oesophagus on reaching the hack of the head gradually enlarges, without differentiation, Into the crop. The crop is the largest part of the entire alimentary canal. It extends half the body length in both species. It is usually distended by food in wild-caught specimens. The distended crop reaches its maximum width at the junc­ tion of the thorax and the abdomen. It then narrows rather sharply Into the proventriculus. The crop is a muscular in which food is apparently retained for an extended period of time (1-2 weeks in C. campbelll). It is probable that some of food occurs in the crop. In fresh the distended crop can be seen to undergo more or less rhythmic churning by the con­ traction of its muscular wall. Histological sections of the distended crop show little of the details of structure of the crop wall. The nearly empty crop, on the other hand, is histologically more informative (Figures 5-8). There are periods of time when the crop contains only a viscous brownish fluid. At this time it is collapsed and becomes nearly a straight tube. The emptying of the crop of solid food apparently occurs prior to . The cutlcular intiraa of the crop bears spines (Figures 5> 6, INT and SPI) in both species. They are visable only under the oil immersion objective and 16

consistently point caudad. Spines were seen only In longitudinal sections, being sparse near the anterior end of the crop and becoming gradually more numerous near the proventriculus. They appear to be more numerous In £. campbelll (Figure 5) than in L. saccharlna (Figure 6); both figures are from the same general area of the crop wall (i.e. approximately midway between the oesophagus and the proventriculus). Similar but more numerous spines are reported in the crop of the Carolina by Tietz (1923). To the writer's knowledge they are not previously reported in Thysanura. -The Proventriculus. In both £j. campbelll and L. saccharlna the proventriculi (Figures 3» 4, PVT) are similar structures closely resembling the proventriculus of the oriental roach (Eidmann, 1924). Like the roach, both have the proventriculus differentiated from the crop into a muscular organ with an anterior part armed internally with six Inwardly directed sclerotized teeth and a pos­ terior part provided with six spiny cushions. A histologi­ cal section of the muscular wall of the proventriculus near the posterior base of the teeth is shown in Figure 9

for Qj l campbelll and in Figure 10 for saccharlna. In £<*. saccharlna the cardiac valve is essentially a funnel-like contractile process projecting into the 17 mesenteron from the posterior end of the stomodaeura. Inside the valve are six folds which apparently effect the closure of the valve on contraction. Ike Mesenteron. (Figures 3, 4, MENT). In C. campbelll (Figure 3) and L*. saccharlna (Figure 4) the mesenteron is a tube-like structure which connects the proventriculus (PVT) with the anterior intestine (AI). The gastric caeca (GC) are conspicuous enlargements at the anterior end of the mesenteron which completely surround the cardiac valve and often extend forward and lie against the proventriculus. In both C. campbelll and saccharlna the gastric caeca vary in size from the usual condition (Figures 3> 4 GC) to a reduced non-branched doughnut-like process in Lj_ saccharlna or a nine-fingered rosette in campbelli. Histologically the gastric caeca in both campbelll and saccharlna display the same cellular structure, being continuous with the remainder of the mesenteron. Diagrams of the appearance of the cells of the mesenteron in cross section are shown for campbelll in Figure 11 and for JL*. saccharlna in Figure 12. In both species the cells are columnar, though indistinct (Figures 11, 12, CC). The inner ends of the epithetial columnar cells in C. campbelll show a striated border which is not shown in 18

Xu. .aa&QjJflKlPq • In both £j_ Campbell 1 and Xu. saccharlna. the cytoplasm appears granular. The nuclei In the colum­ nar cells (Figures 11, 12, N) are centrally, or slightly more distally, located. In campbelll there appears to be a secretory pore (Figure 11, SCP) In the area of the striated border in a columnar cell. Just beyond this at the peritrophlc membrane is shown a round object which could be a secretory sphere (SPH) such as occurs in Odonate larva (Needham, 1897), and In the posterior region of the mesenteron of Collembola (Folsom and Welles, 1906). Snodgrass (1935> p. 363) and Needham (1397) state that the appearance of the epithelial cells of the mesenteron vary greatly according to the state of the digestive processes. Differences in the histology of the digestive cells of C.*. camobelll.and L. saccharlna (as shown in Figures 11 and 12) are probably of no real significance since selection of comparable states of the digestive processes was not attempted in sectioned individuals. Begular columns of epithelial cells are interrupted at intervals by aggregates of reproductive cells called nidi. The nidi are spaced about 12 cells apart in C. camobelll (Figure 11, NID) and about 6 cells apart in L*. saccharlna (Figure 12, NID). Nuclei of the nidi are easily seen but the cell walls are not distinct in either 19

£jl campbelll or saccharlna. The nidus gives rise to regenerative cells which replace the columnar secretory cells (Snodgrass, 1935> P. 363). In both campbelll and saccharlna the epithelial cells appear to be uniform in structure throughout the mesenteron, and slightly longer in the gastric caeca. The peritrophic membrane (Figures 11, 12, PM) occurs in both species, forming an envelope surrounding the food in the mesenteron. Its condition is probably related to the state of the digestive processes. The basement membrane (Figures 11, 12, BM) forms the sheath surrounding the epithelial cells and nidi. It serves as the base for and is the point of contact for the muscular network surrounding the mesen­ teron. The musculature of the mesenteron lies against the basement membrane in both species. The longitudinal muscles (Figures 11, 12, LMCL) lie outside the more numerous circular muscles (CMCL). The Proctodaeum. This portion of the alimentary canal connects the mesenteron to the anus. In both campbelll and L^. saccharlna the proctodaeum consists of the malpighian tubules (Figures 3» MPT), the anterior intestine (Figures 3, 4, AI), the rectum (Figures 3» B) and the rectal gland (Figures 3» BG) which surrounds the rectum at the anus. 20

The malpighian tubules (Figures 3, k , (MPT) are four in number In both species and have their insertion just anterior to the constriction marking the beginning of the anterior intestine (Figures 3» AT). Malpighian tubules in both campbelll and L. saccharlna may be seen in motion in fresh dissections in saline. In campbelll tftfci bubules are about equal to the body in length while in saccharlna they are about twice the length of the body. They are slightly brownish in color in both species and become tapered near their free ends becoming nearly transparent. The malpighian tubules are tracheated in both species by four tracheal branches from the mesenteron, one branch following each tubule to its end. The malpighian tubules in cross section appear as thick-walled tubes in both species (Figures 15, 16). In campbelll and cell walls and nuclei stain lightly (Figure 15, W, N). In Lj. saccharlna there is no cell wall differentiation and the nuclei stain very densely (Figure 16, N). From external appearances there is no pylorls in either species to mark the junction of the mesenteron with the anterior intestine. Histological sections, however, show that in iu. saccharlna the mesenteron actually pro­ jects funnel-like into the anterior intestine and that 21 the malpighian tubules penetrate both the anterior Intestine and the mesoderm. The pyloric valve appears to be mesodermal, being an internal mesodermal closure. This differs from the Collembola (Folsom and Welles, 1906) and the Carolina grasshopper (Tietz, 1923), which have the pyloric closure of proctodeal . Snodgrass (1935, p. 377)» mentions the projecting mesenteric epithelium forming the pyloric (ventricular) valve as being known but gives no example. Cox (1939) states that in the blackfly Slmullum. the pyloric valve is of epithelium of the mesen­ teron. The anterior Intestine in both campbelll (Figure 3 , AI) and saccharlna (Figure A, AI) is a simple tube showing no differentiation into parts. It leads from the mesenteron to the rectum without diverticula (other than malpighian tubules). Histologically the anterior in­ testine and rectum of both campbelll (Figure 13) and L. saccharlna (Figure lA) are very similar. Each is made up of a layer of circular muscles (CH.CL) and a few lon­ gitudinal muscles lying inside the circular muscles. (LMCL). The epithelium is a convoluted pad-like thickening of the wall which forms six lobes reaching nearly to the center. Some nuclei in the epithelium of campbelll (Figurel3, N) are rounded and some are angular in outline while in saccharlna (FigurelA, N) they are nearly all 22 rounded. The cuticular intima shows sharp folds in C. campbelll (INT) while in saccharlna the cuticular intima is smooth. The basement membrane lies.between the Intima and the muscular tissue in both species. (BM). The rectal gland (Figures 3» RG) In both C. campbelll and L*. saccharlna is shown in histological longitudinal section in Figures 17 and 18 respectively. They are similar in both species, having much convoluted epithelium (Figures 17, 18) with few scattered nuclei, and like the anterior intestine and rectum have no cells differentiated. There are two valves associated with the rectal gland, one at the anterior portion of the gland (Figures 17, 18, VLV), and the other being the anus. The cuticular intima (Figures 17, 18, INT) is continuous from the rectum, through the rectal valves to the anus. The valves (Figures 17, 18 VLV) are actuated by sphincter muscles (CMCL). In a live C. campbelll the rectal gland was observed to be in a state of fairly rapid churning movements. Rectal glands are organs about which little is known (Snodgrass, 1935 > P. 381).

The salivary glands occur in both Cj. campbelll (Figure 3> SG) and saccharlna (Figure SG) as lobed organs in the head and thorax. They are nearly colorless and have a very delicate covering membrane, making them 23 difficult to find by dissection. Snodgrass (1935, p. 15*0 says that since the function of "salivary glands" is variable, and in most Insects, poorly known, the term labial glands would be more appropriate. Histologically the salivary glands in both C. campbelll (Figures 19, 20) and L. saccharlna (Figure 21) are complex.

Figures 19-21 are of comparable forward head lobes of the salivary glands of three individuals. The figures represent the microscopic fields using the 1.8 mm oil immersion objective and the 10X ocular. By comparing Figures 19 and 20 (of two individuals of

Qju campbelll) it can be seen that a wide difference in appearance occurs in the salivary gland in one species. The large number of spheres in Figure 19, compared to the small number of spheres in Figure 20 (SPH) suggests a cyclic (or mass discharge) function of this gland asso­ ciated perhaps with the cycles of digestion related to ecdycis. The relatively more numerous and much smaller spheres in the salivary gland of L*. saccharlna (Figure 21, SPH) indicates a probable difference in structure between species. THE CENTRAL NERVOUS SYSTEM (Figures 22, 23)

In £ju campbelll (Figure 22) and in L*. saccharine (Figure 23) the central nervous system consists of a brain (BR) and subocsophageal ganglion (G) in the head, a ganglion in each thoracic segment, and eight abdominal ganglia (G, 1 - S), all interconnected by two longitudinal cords, the connectives (Figures 22, 23, CN). In addition there are nerves (Figures 22, 23, N ) which radiate from the ganglia to the various parts of the body. The brain is joined to the suboesophageal ganglion by a connective on either side of the oesophagus. With the exception of the brain and its connectives to the suboesophageal ganglion, the central nervous system lies ventrally in the body cavity, and is known as the . The number of ganglia in the ventral nerve cord as found in campbelll and L,. saccharlna represents a primitive condition in the class Hexapoda, no insect ever having more except in the embryo (Schro dor, 1928, Figure 4o). Weber (1933, P» 256) says the primary number of ganglia in the insect embryo is 20.

24 25

In Figures 22 end 23 the arrows represent schematic­ ally the paths of the tracheae from the spiracles at the outer margins of the segments to the ganglia. The dotted lines represent schematically the nerve connections of the body segments to the ganglia. The usual change which takes place in the ventral nerve cord as insects have evolved to higher forms has been a reduction in the number of ganglia by coalescence. In the Carolina grasshopper, for example, there remain only five abdominel ganglia (4 - 8), abdominal ganglia 1 - 3 having united with the ganglion of the mete thorax (Snodgrass, 1935, p. 477 and Figure 247). Snodgrass (Loc. cit.) says that when a ganglion migrates, it continues to Innervate consistently the segment from which it had its origin. ’’Hence (says Snodgrass) morphologically, a ganglion should be numbered according to the segment it innervates."

In Lj. saccharine (Figure 23) there has been no migration of ganglia. Each ganglion lies within its home segment, innervates that segment, and receives its tracheetion from the ventral commissure (if present) of that segment (Sulc, 1937). The central nervous system of_L. saccharine has been figured by Hilton (1917). He did not show the placement of the ganglia relative to body segmentation. 26

In G_. campbelll (Figure 22) there hea been a forward migration of ganglia. Abdominal ganglion 1 haa migrated forward into the metathorax where it liea partly fuaed to the metethoraoic ganglion. It ia trachea ted by a- branch from the ventral coramiaaure of the metathorax. Thia ganglion innerve.tea abdominal aegment 1. Abdominal ganglia 2 -5 have each migrated forward one aegment ao that they lie within segmenta 1 -4 respectively. The ventral commisaure of aegment 2 haa tracheal branches leading to abdominal ganglia 2 and 3. The ventral commissure of segment 3 has tracheal branches leading to abdominal ganglia 3 end 4. The ventral com­ missure of aegment 4 haa tracheal branches leading to ebdominal ganglia 4 and 5. Abdominal ganglia 2 to 5 continue to innervate segmenta 2 to 5. Abdominal ganglia 6 to 8 have not migrated; each is trachea ted by branches of the ventral commissure of its own segment end each innervates its own segment. Abdominal ventral commissure 8 however, has (in addition) tracheal branches extending cephalad to abdominal ganglion 7. The changes in relationship of body segmenta, nerve, and tracheal connections to migrating ganglia is seen by comparing campbelli (Figure 22) and 1^. aaccharina (Figure 23). In sacoherina there is no migration of ganglia and each segment is Innervated by, end tracheates, its own ganglion. In £j. campbelll migration of ganglia ha taken place, the nerve connection between body segment and removed ganglion is maintained, but the tracheation suffers change. A trachea may desert a migrated ganglion (the trachea of segment 1). A trachea may branch to a ganglion not previously served by it but which has moved into the neighborhood (the trachea of the metathorax serving abdominal ganglion 1). The nervous system and the respiratory system are both of ectodermal origin. The central nervous system is laid down at an early period in the embryo, each ganglion establishing its segmental connections before migration and coalescence takes place. The tracheal system is formed at a later period in the embryo either concurrent or subsequent to migration and coalescence of the ganglia. Thus the mechanism of the changes in the relationship of body segments, nerve, and tracheal connec­ tions to migrating ganglia as exemplified by C^. campbelll (Figure 22) can be explained on the basis of known facts. THE DOHSAL VESSEL

(Figures 2b - 32)

The dorsal vessel in campbelll (Figure 2*0 and lit saccharlna (Figure 2 5 ) is a tube-like structure located at the mid-dorsum, and reaching from the tip of the abdomen to the base of the brain in the head.

Snodgrass (1935> P. 399) indicates that the division of the dorsal vessel into heart and is usually on the basis of pusatlle and non-pulsatile portions respec­ tively. He further states that, at best, the distinguish­ ing features of heart and aorta are difficult to define.

In campbelll and L*. saccharlna the dorsal vessel is pulsatile throughout its length. The body fluid flows cephalad in a continuous stream, and apparently is not interrupted by any phase of the pulsatile cycle. The diastolic phase of the pulsation is comparatively rapid, while the systolic phase of the pulsation is comparatively slow.

In both species there appears to be a thoracic flap-like valve (TVL) (seen only during pulsations) which divides the entire dorsal cavity into a anterior chamber

(ACH) and a posterior chamber (PCH). In C. campbelll. this valve is in the posterior part of the prothorax, and,

28 f

29 in saccharlna is near the center of the raesothorax. When the posterior chamber is in systole, the thoracic valve is open and the anterior chamber is in diastole; when the posterior chamber is in diastole, the thoracic valve is closed and the anterior chamber is In systole. This mechanism of the insectan heart-beat cycle is not recorded elsewhere, to the writer's knowledge. Even though the posterior chamber of the dorsal vessel in campbelll and saccharlna appears to be chambered more or less corresponding to body segmentation, the posterior chamber contracts as a unit, there being no (or very slight) . Grassi (1887) shows the dorsal vessel of Japvx as being open on the posterior end. In Cj. campbelll and L. saccharlna the posterior end of the dorsal vessel appears to be closed. In histological sections, the terminus of the dorsal vessel was found to lie above the rectal gland near the extreme tip of the body cavity. Figure 30 shows a section of the dorsal vessel of £*. campbelll near the posterior tip and Figure 31 shows (in the same insect) the most posterior section in which the dorsal vessel appears. The penultimate serial section of the posterior of the dorsal vessel in .1^ saccharlna is shown in Figure 32. According to Snodgrass (1935* P* ^01) the posterior end of the dorsal vessel is generally closed. 30

Histologically, the dorsal vessel in both species (Figures 26, 27) shows strieted muscular well (W). Snodgrass (1935, p. 401) spys that contractions of the heart ere "...undoubtedly produced by the muscles of the heart walls." The intima (Figures 26, 27, INT) forma the lining of the dorssl vessel pnd an adventitious membrane (AM) forms an outer sheath. The pericardial sinus mem­ brane (Figures 26, 27, PSM) separates the dorsal vessel from the body cavity. Due to the difficulties inherent in dissection of the dorsal vessel in saocharina. the ostia (which 8re no doubt present) were not seen. The dorsal vessel of c . campbeHi, on the other hand, was observed without dissection due to the unusual transparency of the body well. By confining the insect between the concavites of two microscope slides, ostia (Figures 24, 28, OST) in the pulsating heart of campbe Hi were observed. The ostia are extremely thin, paired, pocket-like valves. They open (Figure 28-A) at the beginning of diastole and close (Figure 28-3) at the beginning of systole. The arrows in Figure 28 indicate the direction of fluid move­ ment . Ostia in C. campbelll (Figure 23, OST) were seen in the heart chamber of the mesothorax, the mete thorax, and the first eight abdominal segments. 31

Pericardial cells occur typically in the pericardial sinus where they form masses or strands on either side of the heart (Snodgrass, 1935, P. *H5)« They are believed to be excretory in function since they precipitate carmine in their cytopl asm (Snodgrass, 1935, p. ^15). In £L*. campbelll the pericardial cells (Figure 2'+, PC) occur in paired groups lying directly on the walls of the dorsal vessel and the body of the pericardial sinus. They occur more or less near the ostia and thoracic valve of the dorsal vessel. The pericardial cells in Leolsma sacharlna were described by Bruntz (1908, Figures 11, 12) as closely associated with the dorsal vessel. Hollande (1922) con­ siders these cells to have an important physiological function in that they have the property of occluding colloids such as India ink, and of precipitating ammonia carmine. Hollands believes they convert colloids into crystalloid compounds which are transferred by the to the malpighian tubules where they are excreted. A remarkable clustering of these cells occurs through­ out the dorsal vessel in some individuals of L*. saccharlna. These thickly clustered cells are shown in Figure 29 for abdominal segments 2 and 3 in such an individual. They cluster on either side of the heart wall, even spanning the heart at the point of attachment of the alary strands. THE REPRODUCTIVE ORGANS (Figures 33 - 54)

Meting in silverfish hes never been observed. Spencer (1930) hes described the process of primitive fertilize- tion in Thermobie domes ties (Peckerd) (Lepismetidee) in which e. sperme tophore is discherged by the mele rnd picked up by the female efter r prolonged "love dence". It is probeble thet sperm trrnsfer from mele to femele is eccomplished in cempbelll rnd seccherine by e similer mechenism.

The interne 1 reproductive orgens in L. secchrrine have been described in limited deteil (Peckprd, 1898, Figures 458-9, Schroder, 1928, p. 481, Weber, 1933, Figures 445e end Greasi, 1897 Figure 41). L_. seccherine is included, however, in this study. The Femele (Figures 33, 37, 41, 42). The in

C. cempbelll (Figure 33 CV) end in L_. seccherine (Figure 35 OV) ere peired orgens lying on either side of the ebdomen. Eech overy consists of five folliculer egg tubes (ovrrioles) (CVL) of the penoistic type, there being no speciel nurse cells present. Eech ovariole is etteched by e pedicle (PCL) to e common tube, the oelyx (CLX) which in turn, becomes the oviduct (CVD) end which is Pttached on either

32 33

side of the (SPT) at the base of the ovipositor (OVP). Marked differences between species are that the oviduct Is much longer In campbelll. and the calyx Is more specialized in L. saccharlna (Figures 33, 3*4-, OVD, CLX).

Each ovariole contains a number of egg follicles (EF) of different sizes, the largest being at the pedicle. The follicles become progressively smaller anteriorly, and end In the terminal filament (TF). C. campbelll has a small number of egg follicles which taper rather abruptly into the terminal filament (Figures

33» 41, EF, TF). Xul saccharlna has a larger number of egg follicles which taper gradually into the terminal fila­ ments (Figures 34, 42, EF, TF). The terminal filaments of an in each species end at a single point near the thorax. The nuclei extend into the terminal filaments (perhaps to their ends) (Figures 41, 42, N). The spermatheca (Figures 33 - 36, SPT), is an oval organ which lies ventrad of the ganglia of abdominal segments 7 and 8. Figures 35 and 36 are of sections made longitudinally through the exact center of the insect.

Figures 35 and 3 6 are slightly schematic in that the oviduct (OVD) is shown inserted from the top Instead of from both sides as it actually occurs. The spermatheca 34 is called "bursa copulatrice" by Grassi (1887) and "Eiergang plus Vagina" by Weber (1933, p. 479). Struc­ turally the spermatheca in each species appears not to be accessible to copulation and not to be so oriented as to be a passageway for the eggs. Active sperm were found, by dissection, in the spermatheca of campbelll. It is highly probable the spermatheca in L*. saccharina also contains sperm. The path taken by the sperm in their transmission to the spermatheca is probably through the duct opened by the downward movement of the eighth sternite (Figures 35, 36, STg). The writer terms this duct the sperm recep­ tacle (SPR). It is probably this device which enables the female to pick up and retain the spermatophore.

The Male (Figures 37 - 40, 42 - 54). The reproductive organs of the male are more complex than those of the female.

Three pairs of testes occur on each side of the abdomen (Figures 37, 38, T). Each pair is connected by the vas efferens (VE) to a common duct the vas deferens

(VD) which enlarges posteriorly into an oval seminal vesicle (SV) that serves as a reservoir for sperm. From the seminal vesicle on each side of the abdomen, the sperm tube (vas deferens) folds variously, enlarges into accessory gland tubes (AG), and is attached at the 35 base of the sedeegus (AED) which arises from the posterior margin of abdominal sternite 8. The arrangement of the last paired loops of the accessory glands is not bilaterally symmetrical. The loop

on the right is inserted beneath abdominal ganglion Gq and the corresponding loop on the left lies above the ganglion. The difference in gross enatomy between species is small. In Q. campbelll the length of the internal male organs is about twice that of the body, while in L. sa ocherlna the length approximately equals that of the body. The testes in both species are transparent in fresh dissections except for a white opacity marking the presence of mature sperm near the vas efferens. Histologically the testes (Figures 39, 40) show a marked difference in appearance in the two species. The essential difference lies in number end arrangement of the maturing germ cells. The germ cells in C_. campbe 111 appear fewer in number and are larger than in saccharine. In both species the germ cells in the germarium (GM) sppear as nuclei only. They appear as cells in the zone of growth (ZG).

In the maturation zone of the testis (Figures 39, 40, MZ), 0. cempbelll apparently matures a single sperm cyst 36

(SPC) et a time while in saccharine several are matured simutaneoualy. The parent germ cell (which Snodgrass terms the

’’epical cell”) is found near the tip of eech testis ps a smell group of specialized cells (Figures 40, 45, APG). According to Carson (1945) these ere common in the Orthoptera but have never been reported in Thysenura. The seminal vesicles have muscular walls (Figures 43, 44, MCL) and contain granular substrate and sperm. In C. cempoelll (Figure 43) the seminal vesicle appears to contain disorientated sperm (SP) while the sperm in the seminal vesical of L_. saccharine (Figure 44, SP) appear to be oriented, probably due to attachment of the sperm in bundles. Histologically, the vase efferentia end vase defer- entia, bear slight resemblence to each other, either within a species or between species (Figures 47 - 50). They differ in number and arrangement of nuclei (N), relative density of cytoplasm (CYT), end relative external and internal dimensions of the whole tube. The accessory glands histologically (Figures 46, 51, 52) present a most varied appearance, being apparently "built in" to the relatively large accessory gland tubes (AG). It is probably in these glandular tubes that the 37 sperm are prepared for transfer to the female. The accessory gland tubes in both species are made up pre­ dominantly of reticular tissue such as shown in Figure 46 for Xu. Figures 51 and 52 are examples of the histology of the accessory gland tubes (Figures 3 7 , 38, AG) from the same relative position (X) in campbelll and Xu. sac­ charlna respectively. Snodgrass (1935» PP. 583-5), in discussing male genitalia with paired , Includes the , Ephemerlda, and Dermaptera only, and says, there is no suggestion of a double origin of the penis in any of the apterygote insects. Figure 53 shows in campbelll the continuity of a pair of orifices from the Internal accessory gland tubes (D) outward through the body wall (C) and continuing to the tip of the aedeagus (B and A). A similar group of cross sections is represented for L. saccharlna in Figure 54, A - D, differing from C. campbelll in having a single body wall opening (3). These findings would seem to establish a probable double origin for the aedeagus in the Apterygota. ABBREVIATIONS USED ON FIGURES

A antehnal AC assymmetric connective ACH anterior chamber ADC anterior dorsal connective AED aedeagus AG accessory gland tube AI anterior intestine AL antenna-labrum AM adventitious membrane APG apical cell group AS alary strand AV abdominal ventral BM basement membrane CC columnar cell CDB cephalic dorsal branch CLX calyx CMCL circular muscle CN connective CR cercus CVB cephalic ventral branch CYT cytoplasm DA dorsal arch

38 E epithelium EP egg follicle PM femoral muscle PT frontal trachea G ganglion GC gastric caeca GM germarium

H head INT intima L labrum LMCL longitudinal muscle LP labial palpus LT leg trachea

LVP long ventral fork MB mandible MCL muscle

MNT mesenteron MP maxillary palpus MPT malpighian tubule MS mesothorax

MT metathorax MTVC metathoracic ventral commissure MV metathoracic visceral branch MVB metathoracic ventral branch MVC mesothoracic ventral commissure MZ maturation zone N nucleus ND nidus NV nerve OB ocular branch OE gonopophyses segment 8 OM ocular-manidbular ON gonopophyses segment 9 : OST ostium OV ovary OVD oviduct OVL ovariole OVP ovipositor P prothorax PC pericardial cells PC II posterior chamber PCL pedicle PDC posterior dorsal connective

PL paranotal PM peritrophic membrane PR proctodeum PSM pericardial sinus membrane PT prothoracic tracheal trunk PV prothoraclc visceral PVC prothoracic ventral commissure PVT proventrlculus R rectum RG rectal gland S spiracle SCP secretory pore SG salivary gland SP spiracular pit SPG sperm cyst SPH sphere SPI spine SPM sperm SPR sperm receptacle

SPT spermatheca ST spiracular trunk STN sternite STO stomodeum STY stylus

SV seminal vesicle T testis TF terminal filament TVL thoracic valve 42

VD vas defersnae VE vas efferens VB ventral branch VC ventral commissure VSB visceral branch VF visceral fork VLV valve VT visceral trachea W wall

X poition of sections Figures 3 7 , 33 shown in Figures 51 and 52. ZG zone of growth 1-12 abdominal segments 1-12 43

Figure 1. .Tracheation of the head, thorax, and first abdominal segment of £*. camobelll. reel

DA

vr ADC

VF, -VF PDC MVBj

DA MT MTV<

AOi

44 Figure 2. Tracheation of the abdomen of C. camobelll. 46 i+7

Figure 3. Gross anatomy of the alimentary canal of C. camobelli. Figure Gross anatomy of the alimentary canal of L. saooharlna.

Figure 5. Histological longitudinal section of the wall of the cron in C. camobelli. Figure 6. Histological longitudinal section of the wall of the croo in L. saccharina.

Figure 7. Histological cross section of the crop wall in C. camobelli. Figure 8. Histological cross section of the crop wall in saooharlna. MENT 49

Figure 9. Histological cross section of the proventricular wall in C. cam-Dbelll. Figure 10. Histological cross section of the proventricular wall in L. saccharina.

Figure 11. Histological cross section of the wall of the mesenteron of C. camobelli. Figure 12. Histological cross section of the wall of the mesenteron of L. saccharina.

Figure 13. Histological cross section of the wall of the rectum of C. canrobelli. Figure 14. Histological cross section of the wall of the rectum of L. saccharina.

Figure 15. Histological cross section of a malpighian tubule in C. canrobelli.

Figure 16. Histological cross section of a malpighian tubule in L. saccharina.

Figure 17. Histological longitudinal section of the rectal aland of C. camobelli. Figure 18. Histological longitudinal section of the rectal gland of L c spcph^rina. CMCL LMCL LMCL MCL

LMCL4 CMCL' LMCli \ CMCL

wm0w

50 51

Figure 19. Histological section of salivary gland lobe of camobelli. Figure 20. Histological section of salivary gland lobe of Cjt camobelli from another individual. Figure 21. Histological section of salivary gland lobe of It*, saccharina. 52 53

Figure 22. Gross anatomy of the central nervous system in camobelli. Figure 23. Gross anatomy of the central nervous system in li*. saccharina. In Figures 22 and 23, the arrows indicate source of tracheation and dotted lines indicate segmental innervation. • • ••• CM CM 55

Figure 24. Gross enetomy of the dorsal vessel in 0. cempbe Hi. Figure 25. Gross enetomy of the dorsel vessel in secoherine. Figure 26. Histologicel cross section of the dorsel vessel in G. cempbelli. Figure 27. Histologicel cross section of the dorsel vessel in L. seccherine. Figure 28. Ostium in open position (A) in closed position (B) in the dorsal vessel of G. cempbelli (diagrammatic), errows indicate direction of fluid flow.

Figure 29. Gross enetomy of pericardial cells of the dorsel vessel in segments 2 end 3 of L. seccharina. Figure 30. Histological section neer the posterior tip of the dorsal vessel in C. cempbelli. Figure 31. Histological section of the posterior tip of the dorsel vessel in C. cempbelli. Figure 32. Histological penultimate seriel section of the posterior terminus of the dorsel vessel of L. seccherine.

57

Figure 33. Gross anatomy of the reproductive organs of the female S L u camobelll. Figure 3^. Gross anatomy of the reproductive organs of the female J**. saccharlna. Figure 35. Histological sagittal section of the posterior of the abdomen of the female camobelll. Figure 36. Histological sagittal section of the posterior of the abdomen of the female saccharlna.

59

Figure 37 Gross anatomy of the reproductive organs of the male £jl camnbelli. Figure 38 Gross anatomy of the reproductive organs of the male L*. saccharlna.

Figure 39 Histological longitudinal section of a testis of £*. Campbelli. Figure ^0 Histological longitudinal section of a testis of Ji*. saccharlna.

61

Figure 41. Histological section of the tip of the ovariole of £L*. campbelll. Figure 42. Histological section of the tip of the ovariole of'Ii,. saccharlna. Figure 43. Histological section of the apical cell group in the testis of C ^ . Campbell 1 . Figure 44. Histological cross section of a seminal vesicle of Campbell!. Figure 45. Histological cross section of a seminal vesicle of L*. saccharlna. Figure 46. Histological cross section of glandular reproductive tube in the male L*. saccharlna. Figure 47. Histological cross section of a vas efferens of Campbell!. Figure 48. Histological cross section of a vas efferens of 1^. saccharlna. Figure 49. Histological cross section of a vas deferens of Qj. Campbell!. Figure 50. Histological cross section of a vas deferens of saccharlna. Figure 1. Histological cross section of a glandular reproductive tube in the male £ju campbelll. Figure 52. Histological cross section of a glandular reproductive tube in the male L*. saccharlna. 62 63

Figure 53 Selections from serial cross sections from the neighborhood of the base of the aedemas in C. canrobelll. A and B the aedeagus, B, being 60 microns cephalad of A, the body wall (C) 4o microns cephalad pf B, and the accessory gland tubes (D) 50 microns cephalad of C. Figure 5^ Selections from serial cross sections from the base of the aedeagus in L*. saccharlna. A the aedeagus, B-D consecutive 10 micron sections through the body wall at the base of the aedeagus, B,' 110 microns cephalad from A, D the accessory gland tubes. O) •N SUMMARY

The Internal anatomy of two species of silverfish Ctenoleolsma campbelll and Leolsma saccharlna is described and related to other insect forms.

The respiratory system is similar in the two species, each having ten pairs of spiracles all interconnected by means of dorsal connectives and ventral commissures. They differ in the manner in which the eye is tracheated, in the disposition of vestigial stylal tracheae, and by the absence of the ventral commissure in abdominal segment eight. In camobelll tracheal branches do not consis­ tently follow migrated ganglia. The alimentary canal is similar to that in Orthoptera and is much alike in the two species. It follows a generalized plan, being little longer than the body. It Is readily differentiated into stomodeum, mesenteron, and proctodeum, having salivary glands in head and thorax, spines in the wall of the crop, a muscular proventriculus with sclerotlzed teeth, gastric caeca, four malplghian tubules, rectum, and rectal gland. The alimentary canal is periodically cleared of food preparatory to a molt. The central nervous system is similar in both species. It consists of a brain, sub oesophageal ganglion, three

65 • 66 thoracic ganglia, and eight abdominal ganglia, all inter­ connected by the longitudinal cords. The central nervous systems differ in that, in campbelll. abdominal ganglia one to five have migrated forward one segment, no migra­ tion having occurred in L*. saccharlna. A migrated ganglion continues to innervate the segment from which it came, while it may or may not preserve a tracheal connection with that segment. This difference in behavior of tracheae and nerves in their relationship to a migrated ganglion is apparently related to the sequence in which these structures are formed in the embryo. The dorsal vessel in both species is pulsatile throughout its length. It acts as a two-chambered pump, the chambers being separated by a thoracic valve. When the anterior chamber is in systole the posterior chamber is in diastole, and vice versa, no peristalsis being noticeable. Pericardial cells are present in both species but are much more numerous in L*. saccharlna. Ostia are probably present in both species but are difficult to see. They were seen only in campbelll. Ten pairs were counted through the transparent body wall. The in both species is relatively elaborate, pointing to an inefficient means of sperm 67

transfer to the female, namely, by spermatophore Instead of copulation. The female organs consist of a pair of ovaries, each with five egg tubes, connected to a common duct near the base of the ovipositor. The spermatheca lies beneath the eighth abdominal ganglion and communicates with the ovi­ duct, ovipositor, and genital pore above the eighth abdominal stcrnite. The male organs consist of three pairs of testes on either side of the abdomen, the testes on each side being connected by a single tube to a seminal vesicle, thence through an elongate tube to the base of the aedeagus. Accessory glands appear to be built into these tubes. There is gn assymmetry in the arrangement of these tubes at the base of the aedeagus in that one loops beneath the eighth abdominal ganglion while the other of the pair loops above it. Apical cells are believed to be present, not having been known for Thysanura. Histological sections of the aedeagus and its base provide evidence, not previously known, for a paired origin of the aedeagus in the Apterygota. LITERATURE CITED

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