GERM CELLS IN TATUSIA NOVEMCINCTA 349 



the four embryos which are to develop in the diverticula of this 

 same vesicle. The failure to find germ cells at this time may be 

 due to one or more of several causes. It is possible but not 

 probable, that grerm cells at this early period, even though 

 present, have not yet assumed the form which in future stages 

 become so constant and reliable for identification. Moreover, 

 the somatic cells at this time are larger than later, having 

 undergone fewer divisions — thus making it less easy to distin- 

 guish, by size relationship, the germ cells from surrounding 

 cells. Again, it may be questioned whether the germ cells arise 

 at all before the appearance of the primary embryonic rudi- 

 ments — such a suggestion excluding the possibility of a common 

 origin for germ cells in a polyembryonic form. It will be remem- 

 bered that vSwift ('14) in his study of the chick arrives at the 

 (Conclusion that the germ cells arise at the time of the primitive 

 streak in a specialized region of the germ wall. That is, he 

 believes that certain entodermal cells of the germ wall at this 

 time are producing, through division, germ cells which cytologi- 

 cally are similar to, the cells of the germ wall. Thus, according 

 to Swift, earlier than the primitive streak stage, germ cells, as 

 such, are not to be found. Whether or not this fact, unmodified, 

 holds true for the armadillo, notwithstanding that a few germ 

 cells may be seen before embryonic primordia appear, is a 

 question. It is the desire of the writer to demonstrate that in 

 all probability not only the time, but the mode ol origin of 

 germ cells in the armadillo is similar in most respects to that 

 described by Swift for the chick. 



MIGRATION OF GERM CELLS 



Although the germ cells in the stages just described may be 

 in the act of migrating, it seems best to discuss them merely as 

 in the condition found in early stages, and to describe the mi- 

 gration as beginning with the secondary bud stage, from which 

 time the wandering may more surely be followed. In speci- 

 men 290, representing , an early secondary bud stage (fig. 3a), 

 the germ cells have become more numerous and are located on 

 the entoderm a little lateral to the primitive streak region which 



