622 SIDNEY I. KORNHAUSER 
as emanating from the nucleus of the growing odcyte. After 
fertilization the division of the cleavage nucleus gives rise to a 
number of nuclei, and these possessing complete diploid sets of 
chromosomes migrate to various parts of the cytoplasm which 
become more and more specialized as development proceeds. 
This specialization becomes rigid, as shown by the experiments 
on centrifuging insect eggs, destroying portions of developing 
eges (Hegner, 717). In the latter class of experiments, the 
uninjured portion continues to develop and forms only that 
part of the embryo which would be formed by it in a normal 
egg. However, we do not believe that even in insects the cells 
of the embryo act as independent units, although this condition 
becomes almost realized in the formation of the adult. In the 
embryo the cells codperate to form various organs, and there 
must be some vital intercellular connection. As development 
proceeds in an insect egg the internal mechanism of the indi- 
vidual cells seems to be of the greatest importance in shaping 
the most highly differentiated tissues of the adult. Crampton 
(99) showed this nicely in his lepidopteran experiments. Hypo- 
dermis grafted onto a transforming pupa of another species or of 
opposite sex developed as it would have in the individual from 
which it came, as shown by the pigmentation and cuticular 
out-growths of the ingrafted portions. 
Must we not also look upon the development of sex in an indi- 
vidual as a continuous series beginning with the differentiation 
of the gonads, proceeding in the formation of the important 
accessory sexual organs and culminating in the expression of 
various specific secondary sexual characteristics? Those sexual 
differences old phylogenetically are developed early in ontogeny 
and each of the more recent genes affecting sexual characteristics 
must be dependent upon the entire series of changes which 
preceded. Every cell of the individual possessing a complete 
set of chromosomes probably has a double set of genes repre- 
senting the total hereditary basis of the species. There is a 
single exception to this, namely, that in the male the genes 
located in the x-chromosome are present only once. We know 
from the various lines of evidence presented on pages 539 to 
