348 AIMEE S. VANNEMAN 



2, two germ cells are portrayed, one in the process of division. 

 They will be seen to be connected by a frail strand of tissue to 

 the entodermal layer. A further examination of the series of 

 sections reveals the fact that some of the entodermal cells are 

 cytologically very much like the germ cells. A study of young 

 stages suggests that germ cells undergo a considerable number 

 of divisions up until the period when they are seen to enter the 

 gut entoderm. After this and until they reach the gonad, they 

 remain in a resting stage, evidenced by the fact that dividing 

 cells rarely, if ever, are seen in advanced stages of development. 

 There is a tendency, however, for the student of germ cells to 

 overlook dividing cells and consider them ineligible to the cate- 

 gory of germ cells, just because of the fact that they are divid- 

 ing. This, I believe, is an explanation of the frequent low 

 count of germ cells in earlier stages. That it is not the only 

 explanation in the case of the Armadillo, however, will be shown 

 later. Certainly no small number of divisions must occur in 

 early stages, for the comparison in numbers of germ cells in 

 early and late stages is striking. The small number of germ 

 cells found in no. 247 may be explained partly by the fact that 

 the series was cut 10 micra thick, thus obscuring some cells 

 which in thinner sections might have been visible. Such a 

 thickness in older stages is not so disadvantageous, because of 

 the greater number of germ cells, permitting of just so many 

 more chances of cutting through a cell instead'of just missing it. 

 The stage just preceding that described for no. 256 was care- 

 fully scrutinized for germ cells, but results were fruitless. It 

 might be remarked that the next stage younger in my posses- 

 sion is an early ectodermic vesicle before the shifting of any 

 cells preparatory to lateral plate formation— a stage consider- 

 ably younger in time, even if not in appearance, than no. 256. 

 As a matter of fact it is known that the primary buds do not 

 start to differentiate for a considerable time after the com- 

 pletion of the ectodermic vesicle (Patterson, '13). Unusual 

 interest attaches itself to the study of such an ectodermic vesicle, 

 because of the before-mentioned possibihty of discovering some 

 common place of origin in the vesicle wall for the germ cells of 



