KEIMBAHN-DETERMINANTS 243 
these cells remain in a primitive condition and do 
not undergo the histological differentiations charac- 
teristic of somatic cells, a view which, however, has 
~ been objected to (Eigenmann, 1896). The disap- 
pearance of the keimbahn-determinants and the 
yolk globules of vertebrates during this period have 
suggested that these substances are nutritive in 
function, furnishing energy to the migrating germ 
cells. 
The fact of this long rest period, followed by rapid 
multiplication of the odgonia and spermatogonia 
during which no important specializations occur, and 
later succeeded by the remarkable changes that occur 
in both the odcytes and spermatocytes, has led to the 
suggestion (Montgomery, 1911, pp. 790-792) that in 
the germ-cell cycle there is a series of changes 
parallel with that of the somatic cycle. In the 
development of both cycles preformation and epi- 
genesis proceed at the same time. The chromosomes 
seem to be the preformed elements of the germ cells, 
since they are apparently the most stable constitu- 
ents. The cytoplasm, on the other hand, undergoes 
a series of epigenetic changes such as the formation 
of an idiozome, the development of mitochondria, 
the appearance of a sphere, and the metamorphosis 
of the spermatozoén. 
Finally we must inquire into the fate of the keim- 
bahn-determinants in the male germ cells. Does the 
keimbahn material in these cells increase in amount as 
has been suggested for the odcytes and is it localized 
in the spermatogonia, spermatocytes, or spermatozoa 
