ACCOUNT OF THE GERM- CELL CYCLE 31 



example, in Miastor the single primordial germ cell 

 produces eight ; in the beetle Calligrapha multi- 

 punctata the original sixteen undergo two divisions 

 resulting in sixty-four ; and in the chick Swift (1914) 

 has counted as many as eighty-two at this stage. 



We shall see later that the primordial germ cells 

 are often characterized by the presence of certain 

 cytoplasmic inclusions (the keimbahn-determinants) 

 which are absent from the other cells of the embryo. 

 These inclusions appear to be equally divided be- 

 tween the daughter cells so that each of the eight or 

 sixty-four, as the case may be, is provided with an 

 equal amount of the keimbahn-determinants. 



3. PERIOD OF "REST" AND MIGRATION. By rest 

 here is really meant cessation of division. During 

 this period the germ cells either actively migrate 

 or are passively carried by surrounding tissues to 

 the position the germ glands occupy in the larva. 

 In species possessing two germ glands the germ cells 

 separate to form two groups, with, at least in some 

 cases, an equal number in each group. Thus in 

 Miastor the number in each group is four (Fig. 22) 

 and in Calligrapha, thirty-two (Fig. 37). There is 

 evidence that an active migration of germ cells 

 occurs both in vertebrates and invertebrates. Figure 

 6 shows the positions of the germ cells in four species 

 of vertebrates during their change of position. 

 That the germ cells at this time are actively migrat- 

 ing by ameboid movements is the general opinion 

 of investigators, since frequently these cells are 

 ameboid in shape and the distance between the place 



