Gametogenesis in Cestodes. 
433 
rate types, and furnish very unsatisfactory material for cytological study, 
and especially so for supporting current cytological theory, is insufficient 
reason for neglecting tliem as objects of such study. 
In the study of the sex cells of cestodes one is struck first of all by 
the simplicity of the Spermatozoon. Nowhere eise, so far as I know, save 
in trematodes, is there a sperm with no visible differentiation except 
slight differences in diameter; and this simplicity is frequently associated 
vith an enormous production, especially in some cestodes, where, at a 
certain stage of development, the proglottids are largely filled with the 
testes. It seems not unlikely that this simplicity of structure and large 
production are functionally correlated. In cestodes at least the functions 
of the entire organism appear to be subser\ient in a peculiar degree to 
reproduction. Any method of development therefore which would aid 
in the production of large numbers of sperm would be a functional adap- 
tation. 
Aow the repression of the customary two maturation divisions and 
the development of sperm directly from chi’omatin fragments, would 
certainly be a simplification of spermatogenesis and might readily lead to 
a more rapid, and greatly increased production. While the repression of 
these divisions in the development of the egg, would not necessarily 
lead to a larger egg production, altho it might do so, it would clearly be 
a Conservation of energy, ^yhich energy would then be available in the 
metabolism of the egg, leading perhaps to more rapid growth and increased 
yolk production. As I have already indicated (Young 1919 a) the yolk 
gland is in process of degeneration in cestodes, which loss is compensated 
for by the formation of yolk by the egg itself. Any process therefore 
leading to increased yolk production on the part of the egg, would be 
adaptive in the case of cestodes; even tho running directly counter to 
that by which we may suppose yolk gland and ovary to have been origi- 
nally evolved from a common structure. 
There are several references in the literatm’e to abortive mitoses, 
most of which refer to flat worms, but Hegxer (1914) has described it 
in Copidosoma gelechiae a polyembryonic hymenopteron. In Planocera 
inquilina Patterson and Wieman (1912) have shown that an apparently 
degenerating spindle is merely a contracting spindle preparatory to the 
first maturation division, and suggest that the same may be true of other 
species. In Copidosoma one of the degenerating spindles is apparently 
related to the formation of a definite oocyte and the other to “Keimbahn- 
chromatin”. In cestodes the only explanation of the occurrence that has 
been offered thus far to my knowledge is my own, namely, that it is an 
