790 THOS. H. MONTGOMERY, JR. 
the history of the mitochondria during the fertilization of the 
egg, and especially the behavior of those furnished by the sperm. 
PREFORMATION AND EPIGENESIS IN THE GERMINAL CYCLE, AND 
SEGREGATION OF THE GERM CELLS IN ONTOGENY 
The discussion of embryologists upon preformation and 
epigenesis has treated mainly the phenomena of somatic differ- 
entiation, the factors regulating the growth of the embryo from 
the egg. If it be not too premature to speak of a consensus 
of opinion reached in this discussion, it would be to the effect 
that epigenesis and preformation are not mutually exclusive, 
but that both probably proceed at the same time. 
Here it is my wish to call attention to the fact that in the his- 
tory of the germ cells may be recognized both preformation and 
epigenesis, whereby the germinal cycles offer a certain parallel 
to the somatic. 
In the spermatogenetic cycle a number of spermatogonial 
generations occur, during which the number of the chromosomes 
remains constant and no marked cytoplasmic specializations 
take place. But in the spermatocytes remarkable differences 
arise suddenly: the chromosomes group themselves into gemini, 
the mitochondria increase rapidly in amount, the whole cell 
becomes larger, and frequently the centrioles take on unusual 
forms and positions (as upon the cell membrane). Somewhat 
similar changes occur in the oocytes, and more complex ones, 
owing to the production of yolk substance. The spermatids 
often undergo a marked metamorphosis. As one reviews the 
sum total of these processes the conviction arises that there are 
here in the completest form both preformation and epigenesis. 
The chromosomes are on the whole the most stable parts, appar- 
ently continuous from generation to generation, and though they 
may pass through marked changes in forming the sperm 
nucleus, they later emerge, in fertilization, under the same forms 
that they had previously. On the whole they seem to be the 
particular preformed bodies of the germ cells. But this is 
not the case with certain other cell constituents. For in Eu- 
schistus, which seems to exemplify in main features the sperma- 
