GERM CELLS IK TATUSIA NOVEMCINCTA 355 



germ cells of the future embryo arise before the appearance of 

 embryonic primordia. Indeed, I believe that these early germ 

 cells play but a feeble role in the origin and future history of the 

 germ cells. Therefore, while recognizing that stray germ cells 

 may be found as early as the young primary bud stage, the 

 writer beUeves that the active germ cells of embryonic life arise 

 for the most part at the very early primitive streak stage of the 

 embryos. Such an origin for germ cells is in general, similar to 

 Swift's findings in the chick, both as regards place, method and 

 time. The entoderm of the mammalian blastocyst is analogous 

 to the yolk sac entoderm of lower vertebrates. It is not un- 

 reasonable to suppose that in the armadillo the germ cells arise 

 during the secondary bud stage in the embryonic areas through 

 the influence of the ectodermic vesicle upon the blastocyst ento- 

 derm at the point where the two layers come in contact. Ob- 

 servation seems to confirm this. That the germ cells have 

 not arisen in numbers any earlier may be due to the fact that 

 there exists previous to the early primitive streak stages no inci- 

 dent, such as the coming in contact of ectodermic and ento- 

 dermic layers, to favor the proliferation of germ cells. 



SUMMARY 



1. The germ cells of the armadillo are conspicuously large, 

 and first discernible along the entodermic wall of the blastocyst, 

 just preceding the primary bud stages. They are extremely 

 few in number. The active, embryonic germ cells, however, 

 probably do not arise untrl the time of the secondary bud stage 

 appearing in the vicinity of each of the four embryonic areas. 



2. During early primitive streak stages germ cells are seen 

 dividing, pre\'ious to pushing a way into the entoderm of the 

 future gut region. 



3. After gaining entrance into the gut entoderm, the germ 

 cells are carried in the thickening intestinal wall as, during the 

 somite stages, it rounds up to form a closed tube. 



4. By the time the embryo has attained a length of 4 mm. 

 and has a pronounced cervical bend, the germ cells may be seen 



