Some Problems of Reproduction: a Comparative Study of Gametogeny and Protoplasmic Se- nescence and Rejuvenescence. By Marcus JM. Hartog, M.A., I>.Sc, F.li.S., Professor of Natural History in the Queen's College, Cork. TABLE or CONTENTS. PA&E PAGE t. Introductory 3 Cheetophoracese and Ulva- Scope of Inquiry 3 ceaj .... 12 Bibliography 5 Ulothrix 12 Terminology and Notation . 6 Cylindrocapsa 13 [I. Typical Agamic Reproduction 7 Chlamydomonas 13 Monadinete 7 Desmids, Conjugates, and Myxomycetes . 7 Diatoms 13 Acrasieae .... 8 Volvox, Eudorina . 14 III. The Modes of Karyogamy, Oedogoniacese 14 illustiatedchieflyfrom the (Beak formation com- Protophytes . 8 pared with that of 1. Isogamy, multiple and zoosporange in Chyt- binary 8 ridiese and Saproles- (Euisoganiy, Exoiso- niece) 15 gamy) . 9 Coleochtetece . 16 2. Anisogainy . 10 Melauophycea; 16 3. Hypoogamy . 10 Fucacese 16 4. Oogamy 11 B. Apocytial Forms 17 5. Siphonogamy 11 1. Green or Algal Types . 17 IV. Comparative Gametogeny in Cladophora 17 the Vegetable Kingdom . 12 SipllOUCEB . 18 A. Protophytes and Cellular Sphteroplea 19 Algas.... 12 Vauclieria . 20 VOL. XXXIIIj PAET I. NEW SEE. MAJROtJS M. HAETOG. PAOE PAOE 2. Colourless or Fungal 2. Angiosperms . 36 Types . .20 Male structures (pollen a. Phycomycetes zoospo- and pollen tube) . 36 rete . 20 Cell formations in em- Ancylistese . 20 bryo-sac . .37 Chytridieee (Olpidi- Cellular morphology of opsis, Polypha- mature embryo-sac . 40 gus, Zygochyt- V. Comparative Gametogeny in rium,Tetrachyt- the Animal Kingdom . 41 rium) . .21 A. Protozoa. .41 Monoblepharis . 22 1. Flagellata ... 41 Peronosporese. 22 Euflagellata . 41 Saprolegniese . 23 Cystoflagellata (seg- b. Phycomycetes aplano- mentation of zygote sporem . 26 in Noctiluca) . 41 Entomophthorete . 26 2. JELhizopoda and Heliozoa 42 Basidiobolus . 26 3. Gregarinida (Ophryocys- Mucorini . 27 tis, Monocystis) . 42 c. Higher Fungi . 28 4. Hadiolaria . 43 Lower Ascomycetes 28 5. Ciliata .... 43 Lichens . .28 Free Ciliata and Suc- Higher Ascomycetes, toria . .43 Basidiomycetes . 28 Vorticellinea . 47 Ustilaginese . 28 B. Metazoa . .48 Protomyces . 29 1. Spermatogeny . 48 Uredinea; . .29 First mode. .48 C. Higher Thallophytes . 29 Second mode . 49 1. Floridere . 29 Third mode . 49 Bangiacese . .30 2. Oogeny ... 50 Eufloridete . .30 Peculiarities of mature (Secondary fertilisa- ovarian ovum or tion) . .31 Gametogonium . 50 Corallina . 31 First nuclear changes . 51 2. Characeee . .32 Gametogenic fissions D. Archegoniata . .32 (formation of Oo- 1. Muscineas . .32 sphere and Polar 2. Vascular Cryptogams . 34 Bodies) ... 52 E. SiphonoganiEe (Phanero- "Parthenogenetic ova" gams) . .35 of the Metazoa . 53 1. Gymnosperms . 35 VI. A General View of Gameto- Male structures (pollen geny . .54 and pollen tube) . 35 A. The Reduction of the Chro- Archegonia . .35 matom eres in Gametonuclei 54 SOME PROBLEMS OP REPRODUCTION. PAGE B. The Reproductive Incapa- A. The Modes of Rejuvenes- cityof Obligatory Gametes 5 8 cence. G7 C. The Adaptation of Gametes B. The Advantages of Karyo- to different Fates . .59 gamy as compared with D. Analytic Summary of Gam- Agamy and Apogamy . 68 etogenic Processes . 60 (Alleged Excretion Pro- C. Allogamy and Sex . 70 ceases) . .62 D. The Origin of Sex . 72 VII. The Causes of Protoplasmic E. Paragenetic Processes, Senescence and Ultimate usually comprised under Reproductive Incapacity 64 the term " Partheno- VIII. Protoplasmic Rejuvenes- genesis " . .73 cence, its Nature and Modes. .67 IX. General Conclusions I. INTRODUCTORY. THE curiouB phenomena preceding the maturity of the ovum in Metazoa have been the object of much study and the groundwork of much theory during the last fifteen years. Unfortunately processes occurring in this highly specialised group have been assumed to be typical of all organisms ; the authors who have put forward explanations of what they have seen here have too often sought to extend these explanations to other groups, where the facts are different; they have created homologies where none such exist in Nature, and over- looked those which lay under their eyes. In this way proto- plasmic changes of various origin and functions occurring in Protozoa, Protophytes, and Higher Plants, have been inter- preted as excretory processes, in order to make them fit in with the replacement theories of fertilisation, founded almost exclusively on the formation of the polar bodies in the Metazoan ovum. A careful study of the accessible materials in the gigantic storehouse of facts bearing on this subject has led me to the views which will be found in the following pages, namely : (1) That the most general, but not universal, feature un- derlying the preparations for fertilisation is the specialisation SOME PROBLEMS OP REPRODUCTION. PAGE B. The Reproductive Incapa- A. The Modes of Rejuvenes- cityof Obligatory Gametes 5 8 cence. G7 C. The Adaptation of Gametes B. The Advantages of Karyo- to different Fates . .59 gamy as compared with D. Analytic Summary of Gam- Agamy and Apogamy . 68 etogenic Processes . 60 (Alleged Excretion Pro- C. Allogamy and Sex . 70 ceases) . .62 D. The Origin of Sex . 72 VII. The Causes of Protoplasmic E. Paragenetic Processes, Senescence and Ultimate usually comprised under Reproductive Incapacity 64 the term " Partheno- VIII. Protoplasmic Rejuvenes- genesis " . .73 cence, its Nature and Modes. .67 IX. General Conclusions I. INTRODUCTORY. THE curiouB phenomena preceding the maturity of the ovum in Metazoa have been the object of much study and the groundwork of much theory during the last fifteen years. Unfortunately processes occurring in this highly specialised group have been assumed to be typical of all organisms ; the authors who have put forward explanations of what they have seen here have too often sought to extend these explanations to other groups, where the facts are different; they have created homologies where none such exist in Nature, and over- looked those which lay under their eyes. In this way proto- plasmic changes of various origin and functions occurring in Protozoa, Protophytes, and Higher Plants, have been inter- preted as excretory processes, in order to make them fit in with the replacement theories of fertilisation, founded almost exclusively on the formation of the polar bodies in the Metazoan ovum. A careful study of the accessible materials in the gigantic storehouse of facts bearing on this subject has led me to the views which will be found in the following pages, namely : (1) That the most general, but not universal, feature un- derlying the preparations for fertilisation is the specialisation 4 MABCUS M. HARTOG. of gametes by rapidly repeated divisions of a cell—the gametogonium; (2) That the alleged nuclear excretions in the Metazoan egg and the Ciliate " gamete/' &c, represent true gametes arrested in their development; (3) That the so-called "excretions" of protoplasm in plants are of various kiuds, many of which are homologous neither with the former process nor with one another; (4) That the use of the rapid preliminary divisions is a purely physiological one; that is, to induce by exhaustion the same reproductive incapacity that would otherwise require a long series of slowly repeated divisions. On these lines we can account for all the facts, from the simplest cases of the formation of isogametes to the most peculiar phenomena of oogeny and spermatogeny; phenomena which the sexual replacement theories of Minot, Balfour, and van Beneden, on the one hand, and the more complex replace- ment theory of Weismann, on the other, only profess to explain in the higher groups. The views here put forward are essentially a development and extension of what we may term the "morphological theory" of polar bodies, first enun- ciated by Giard, Biitschli, Whitman, and Mark,1 and advocated especially by the Hertwigs. It will not seem strange that this view has never had full justice done it when we reflect that it is to men who have worked especially at the Metazoa that we owe the greatest debt for shaping our biological theories; and that our gratitude has, perhaps, led us to be too unquestioning in our attitude of discipleship to such re- spected masters as Balfour, van Beneden, and Weismann.2 The exposition of the processes of gametogeny naturally leads 1 Mark was the first definitely to express the view that the polar bodies represent abortive ova ; see " Maturation, Fecundation, and Segmentation of Limax campestris," in 'Bull. Mus. Comp. Zool. Harv. Coll./ vol. vi, 1881. 2 I may say that 1 never doubted that some replacement theory of fertilisation was sufficient to cover the facts, till I read and meditated over Maupas's account of the conjugation of the Ciliata ; and this it was that first weakened'my belief, not only in replacement theories, but also in the " pre- liminary excretion " theory on which the others were founded. SOME PROBLEMS OF REPBODUOTION. 5 on to a consideration of the causes of the individual repro- ductive incapacity of most gametes; of the senescence of the individuals produced in the later generations of a long cycle of fissiparous reproduction ; and conversely of the rejuvenescence induced by karyogamy and other processes, which are classified and discussed. A special section is devoted to those modes of rejuvenescence which have been confounded under the name of " parthenogenesis/' but which we may term " paragenetic;" and a general summary of conclusions closes the present study. To keep the exposition clear and continuous I have abstained as far as possible from controversy. I wish to express my thanks to Professors Mark, G-uignard, Strasbiirger, and Weismann for their communication of reprints of valuable papers not otherwise readily accessible to me. I have not deemed it necessary to give references for facts to be found in every text-book, though I have verified as far as possible every statement from the original authorities. In all other cases I have cited my authority in a foot-note. The following is a list of the text-books and papers of general interest to which I may refer the reader.