238 



do appear to possess direct bearings on the problem have almost all 

 been made without any idea that they tended in any such direction. 



There is no wish to disparage the labours of authors of embryo- 

 logical text-books by the remark that such books have hitherto been more 

 concerned with organogeny than with the development of animal 

 organisms, and it is only rarely that the reader of them has his atten- 

 tion called to anything but the germinal layers and the structures 

 which arise from these. Observations treating of degenerations and 

 disappearances of structures during development, like those of my 

 friend R. S. Bergh^) on Aulostoma, are liable to obtain an incre- 

 dulous reception and to be covered with ridicule because — they do 

 not conform to the germ-layer theory, or because they furnish enigmas 

 to the embryologist in quest of a theory of the mesoderm. 



It would be possible to write a book on Comparative Embryology 

 in which the modes of development of organisms as opposed to organs 

 should form the main theme of the work. This I know to be so from 

 lecturing experiences. 



However, this is all wide of the subject to be treated of here. 

 The object of the present writing is a totally different one. The 

 problem for consideration is, assuming an antithetic alternation of 

 generations to take place in Metazoan development with "aposporous" 

 formation of the sexual generation in most if not in all cases, to show 

 what bearings such a conception may have on the interpretation of 

 certain phenomena that occur in the maturation of the sexual pro- 

 ducts, and, as a corollary to all this, it has been deemed necessary 

 to enquire into the nature of the processes involved in the conjugation 

 of the Protozoa. 



The sequel has culminated in a most surprising result, i. e. in 

 the recognition of the prevalence of one primitive mode of reproduction 

 for the whole of organic nature, and this is of such a character that 

 an alternation of generations becomes absolutely essential to its being 

 carried out. A priori if seemed quite hopeless to expect that our 

 knowledge of the processes of conjugation in the Infusoria, which we 

 owe so largely to the brilliant labours of Richard Hertwig and E. 

 Maupas, would confirm the suspicion that existed of the occurrence 

 of a spore-formation with reduction of the number of chromosomes 

 after a conjugation or antecedent to a new one in this group, but, as 



1) R. S. Bergh , Die Metamorphose von Aulostoma gulo. Arbeiten 

 a. d. Zool-Zootom. Inst, zu Würzburg, Bd. 7, 1885. 



