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 oogonia and spermatogonia 

 during which no important specializations occur, and 

 later succeeded by the remarkable changes that occur 

 in both the oocytes 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 spermatozoon. 



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 oocytes and is it localized 

 in the spermatogonia, spermatocytes, or spermatozoa 



