STUDIES ON GERM CELLS 485 



Finally, we must inquire into the fate of the Keimbahn-deter- 

 minants 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 as a definite, visible substance? We know from 

 the investigations of Meves ('11) that the plastosomes in the 

 spermatozoon are carried into the egg, in the case of Ascaris, and 

 there fuse with the plastosomes of the ovum. Whether Keim- 

 bahn-determinants act in a similar manner is unknown. There 

 are, however, certain cytoplasmic inclusions in the male germ 

 cells which have been compared with similar structures in the 

 oocytes; for example, the chromatic body described by Buchner 

 ('09) in the spermatogenesis of Gryllus (see p. 415), and the plas- 

 mosome which is cast out of the nucleus of the second spermato- 

 gonia in Periplaneta and disintegrates in the cytoplasm (Morse, 

 '09) . That Keimbahn-determinants from the spermatozoon are 

 not necessary for the normal production of germ cells is of course 

 evident, since some of the species with which we are best ac- 

 quainted (for example, Miastor) are parthenogenetic. 



7. CONCLUSIONS AND SUMMARY 



1. The most interesting period in the germ-cell cycle is that 

 extending from the formation of the ultimate oogonia and sper- 

 matogonia to the complete segregation of the germ cells in the 

 developing egg. A little known and important part of this period 

 is that during which, in some animals, visible substances (Keim- 

 bahn-determinants) peculiar to the germ cells, appear, become 

 localized in a definite part of the egg or in certain blastomeres, 

 and are equally distributed among the primordial germ cells 

 (pp. 376-379). 



2. The Keimbahn in animals was first traced in dipterous 

 insects. Keimbahn-determinants appear in the eggs of all 

 Diptera that have been carefully studied. The most detailed 

 reports have been upon Miastor, Chironomus, and Calliphora 

 (figs. 1-2, pp. 380-387). 



