446 Bear'd. — Reproduction in Animals and Plants. 
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 
embryological 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 attention 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 1 on Auto stoma , are liable to 
obtain an incredulous 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 anti- 
thetic alternation of generations to take place in Metazoan 
development with c 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 
1 Bergh, R. S., Die Metamorphose von Aulostoma gulo. Arbeiten a. d. Zool.- 
Zootom. Inst, zu Wurzburg, Bd. VII, 1885. 
