VII. The Ikzternal Anatomy oJ Bdella . BU A . D. MICHAEL.P.P.L.S., F.Z.B., P.B.X.S. Read 16th April. 1896. CONTENTS. Page Psge Introductory Observations . The Reproductive System. Modes of Investigation .................. 477 The Male . Species used .......................... 478 General .......................... 603 Position.’ Characters. and Subdivision of the Testes ............................ 504 Bdellinae ............................ 479 Embedding-sacs .................. 505 Food of the Bdellinse .................. 480 Testicular Bridge .................. 506 Pormer Researches .................... 480 Mucous Glands .................... 507 The Trophi and Mouth.organs . Glandular Antechambers ............ 508 Maxillary Lip and Exoskeleton of Rostrum. 482 Penial Canal ...................... 509 Palpi ................................ 483 Azygous Acceseory Gland ............ 511 Mandibles ............................ 483 Laminated Gland .................. 512 Epipharynx .......................... 483 Air-chambers ...................... 513 Lingua .............................. 484 External Labia .................... 514 The Alimentary Canal and Excretory Organ . Spermatozoa ...................... 514 Pharynx .............................. 485 Course of the Spermatozoa to the Exterior (Esophagus and Sucking-stomach ........ 487 and Functions of Organs .......... 515 Ventriculus .......................... 489 The Female . Exdretory Organ ...................... 489 General .......................... 516 The Salivary Glands . Ovary ............................ 516 General .............................. 492 Oviduct .......................... 517 Tubular Gland ........................ 493 Receptaculum seminis .............. 518 Main common Duct .................... 493 External Labia .................... 518 Reniform Gland ...................... 494 The Respiratory Organs .................... 518 Anterior Gland ........................ 494 The Dermal Glands ........................ 519 Pericibal Gland ........................495 The Endosternite ......................... 519 Aeygous Gland ........................ 496 The Musculature .......................... 520 The Braiu and Nervous System . The External Cuticle ........................ 522 The Brain ............................ 497 Bibliography .............................. 523 The Nerves .......................... 499 Explanation of the Plates .................... 524 TheEyes ................................ 503 INTRODUCTORYOBSERVATIONS . THIS paper contains the results of work extending over a period of more than three yeam. and involving the careful dissection of several hundred specimens. besides the preparation and study of numerous serial sections cut in all directions--i . e.,sagittal. hori- zontal. and transverse . The dissections have been made partly on specimens freshly killed SECOND SERIES.-ZOOLOGY, VOL . VI . 66 478 MR. A. D. MICHdEL ON THE either with boiling water or chloroform; but a large number also have been made on individuals hardened in alcohol and other hardcning reagents : this is advantageous for some organs, but usually in Acari I prefer the fresh specimens. The dissections have mostly been stained on the slide with borax-carmine or picro-carmine. The sections have been made from specimens killed with hot water, fixed with picro-sulphuric acid or Flemming’s fluid, stained on thc slide with haematoxylin (Ehrlich’s), and mounted in balsam. I may say that Plemming’s fluid appears to give somewhat the best results when it penetrates, but that its penetrating power is so inferior to picro-sulphuric acid in the case of Acari that a considerable number of specimens are lost when that reagent is employed. Whereas picro-sulphuric acid can bc relied on to penetrate such Acari as BdeZZa with sufficient rapidity it is probably best to use it, although the results will not be quite equal to really good Flemming’s fluid-hardened specimens. Other reagents which I have tried liavc not, I think, produced an equally satisfactory fixing of the histological condition. The species which I have used has been chiefly Bdek Basteri (Johnston, 7 *), because, through the kindness of Professor Herdinan and the officers of the Biological Station (at Port Erin, Isle of Man) of the Liverpool Nsrinc Biological Committcc, I have received supplies OP large numbers of this species at frequent intervals and at various scasons ; these have enabled me to pursue the etlquiry in a manner which I could not otherwise have done; and I beg to tender my best thanks for the assistance. I was anxious to obtain this species because it is, in my judgment, the best suited for research of those that I know, being large (for a BdeZZa)-its total length isa bout 2.5 to 3 mm., and being also very strong and vigorous, with the parts well developed. I have also used BdeZZa vulgaris, B. cupillata (Kramer), and some others, but could not obtain them in equal numbers or with equal ccrtainty. Wherever in the following paper an organ or structurc is mentioned without the species of BdeZZa being named, it belongs to B. Busteri. I have adopted the name of 23. Busteri for the species because there is no doubt that it is tlie creature described by Johnston under that title in 1847, while it is quite uncertain whether it is the specics referred to by any earlier writer. Thus it has been supposed that B. Basteri is the same species which is called Acurzcs Zongicornis by Linnaeus is his ’Fauna Suecica,’ but this is very doubtful. I hardly see how the opinion is arrived at. Moreover Andrew Murray+ considered that Linnaeus has described a different species under the same name in the ‘ Systema Naturae,’ and that this latter is tlie species to which the name is now generally applied. BdeZZa sunguinea, Trouessart, 1894 (21 ), which that author, following Andrew Nurmy, places in a subgenus MoZgus (Dujardin), is, I think, a synonym; indeed, Trouessart liiolself calls attention to tlie probability of its being so, but was not able to obtain Johnston’s original paper. Trouessart does not describe the hairs on the mandibles, which are important according to Kramer’s tables of the genus, tliercfore I * This figure, and all similar figures throughout the paper, rofer to the list of authorities quoted (Bibliography) page 523. t 4 Economic Entomology : Aptera ’ (London, 1876), p. 143. INTERNBL ANATOMY OF BDELLS. 479 should not like to speak with absolute certainty ; but the palpus of his species is similar to that of 3. Basteri (as I found it), and is not similar to the palpus of any other BdelZa which I know of. Bdella marina, Packard *, is probably also the same species. Eupalws sanguineus, Trouessart t, is also a synonym (according to the author himself). Bdella villosa, Kramer and Neuman $, is either the same species or a very closely allied one; but in the figure the fifth joint of the palpus is drawn a trifle shorter than the second, whereas in B. Basteri the second is a trifle shorter than the fifth ; and the spines at the end of the fifth joint are drawn rather longer than those at the side, whereas in B. Basteri they are about equal in length: these, however, are small points, and the probability that the creatures are identical is increased by the fact that Trouessart received some of his specimens of B. Basteri (sarzgzcinea) from Iceland, and these had the fifth joint of the palpus rather shorter than in the French specimens, so that it seems probable that B. aillosu is at most a local variety. I think there is very little doubt that Bdella arctica, Thorell, 18714, is the same species, although here again the fifth joint of the palpus is said to be slightly shorter than the second. Bdella lapidaria, Kramer, 1881 (I 2. p. 28, Taf. 4. figs. 9, 9 a, 9 b,), and Bdella vulgaris, var. littoralis, Moniez, lS90 (I 5), are both sen-shore species, but they are not identical with B. Basteri ; Trouesssrt suggests that they are probably both the same species. I am also greatly indebted to Mr. M. J. Michael, of the Davos Platz, Switzerland, who has cut the sections which I have used for the present study, and has otherwise assisted me. The Bdellinze are usually considered to be a subfamily of the Trombidiidze ; they are a very aberrant subfamily, and are raised into a family by such acarologists as Canestrini (3), Berlese [I, &c., who elevate the old family of the Trombidiida into an order under the name of “ Prostigmata ” (Kramer). Trouessart (20) considers the Prostigmata to be a suborder, separates the Bdellinze from the Trombidiidze, but unites them with the Eupodinze to form a family “Bdellidze ”; his subfamily “ Bdellinte,” however, conbins the same two genera for which I use the term in this paper, but it also contains one other, Cryptognathus (Kramer), which appears to me to be too different to be included. The two genera which I include in the Bdellina: are Bdella (Latreille, 1797) and Ammonia (Koch, 1842), distinguished according to Canestrini (2. p. 181), following Krarner’s subdivision of the genus Bdella, by the long rostrum and long mandibles with very small chela of Bdella, compared with the shorter rostrum and mandibles and comparatively substantial chelze of Ammonia ; but distinguished according to Berlese (I) by the second and third joints of the palpus being more or less fused, and by the presence of a fifth median eye and the absence of hairs between the claws in * The American Natnralist,’ 1884, pp. 827, 828, fig. 2. t Comptes Rendus de 1’Acad. d. Soi. 1888, t. cvii. pp. 753, 755. $ ‘CAcariden wdhrend der