16^ GERM-CELL CYCLE IN ANIMALS 



definite number is not required, and the germ cells 

 become generally distributed throughout the cellular 

 mass before budding begins, the chances are that 

 every bud will contain one or more germ cells. For 

 example, if germ cells occur in all parts of the blas- 

 toderm of the armadillo, as is quite possible, each of 

 the four embryos must become provided with a por- 

 tion of them. On the other hand, the germ-plasm 

 may be rather widely distributed among the cells 

 and only becomes segregated in germ cells after bud- 

 ding takes place. Careful studies of the germ-cell 

 history in polyembryonic species are much needed 

 and would no doubt produce important results. 



The data presented in this chapter are sufficient 

 to prove that in many insects a complete germ-cell 

 cycle can be demonstrated. There are many species, 

 however, in which no early segregation of germ cells 

 has been discovered even after very careful examina- 

 tion. It is therefore too early to make any general 

 statements for the entire class, but we must base our 

 conclusions regarding the germ-cell cycle upon our 

 knowledge of those forms in which the keimbahn 

 actually can be traced. Finally one point should be 

 emphasized ; in every case the segregation of the 

 primordial germ cells is intimately associated with a 

 substance which can be made visible by proper 

 staining methods. In Miastor this is the pole- 

 plasm; in Chironomus the "Keimwulst" or **Keim- 

 bahnplasma" ; in Calliphora the " Dotterplatte " ; 

 in chrysomelid beetles the pole-disc ; and in parasitic 

 Hymenoptera, the keimbahn-chromatin. The na- 



