354 AIMEE S. VANNEMAN 



broiig-ht out several interesting facts which suggest reasonable 

 conclusions as to the origin of the germ cells in the armadillo. 



It was pointed out in the first part of this papers that no germ 

 cells of the character of those seen in later stages could be found 

 in the wall of the early ectodermic vesicle, a stage which long 

 precedes the laying down of any embryonic primordia. It was 

 thought that possibly such a stage might reveal a definite point 

 along the vesicle wall, where germ cells might be seen to be 

 localized, previous to scattering and migrating into the future 

 embryos. In this sense, one might attribute, in a polyembryonic 

 form, a common origin to the germ cells of all the embryos of 

 one vesicle. This, however, not proving to be the case, an ex- 

 amination of the vesicle next in order of development — that is, a 

 stage where the very beginnings of lateral plates can be dis- 

 cerned — revealed the following fact: that there exist several 

 germ cells lying close along the entoderm wall of the vesicle 

 outside the region of the primary buds. The cytological re- 

 semblance of these cells to adjacent entodermal cells, and the 

 presence of a dividing cell at once suggests the possibility that 

 here, for the first time, germ cells are being proliferated. But in 

 the two primary bud stages examined, there were found present 

 in each blastocyst no more than two germ cells. This condition 

 is in contrast to that of the secondary bud stage when the germ 

 cells are relatively numerous in the region of each of the newly 

 forming embryos. The germ cells of each quadruplet all at once 

 become visible in the respective embryonic areas, without hav- 

 ing been seen to migrate there — except for the few cells seen 

 traveling between the embryonic areas of specimen 290 (text fig. 

 2) . As was mentioned earlier in the paper dividing cells are not 

 infrequent during this period. A consideration of all observations 

 would point to the fact that active germ cells do not arise, at 

 least in any numbers, until the secondary bud stage is reached. 

 The few germ cells appearing before this time may be said to 

 have arisen more or less accidentally in anticipation of the later 

 stage. Some of these cells doubtless migrate towards the em- 

 bryonic areas; others, however, probably degenerate. Cer- 

 tainly their number is too few to warrant the belief that all the 



