352 AIMEE S. VANNEMAN 



During this time they seem to be traveling ventrally in the 

 intestine and are distinctly amoeboid in shape (fig. 8). They 

 are elongated and appear to be slightly smaller than before, due 

 no doubt to the crowding among large entodermal cells. At 

 no time durmg the history and development of the armadillo 

 have germ cells been found in the blood vessels. Figure 6 shows 

 the position of the germ cells in the seven, ten, and fourteen 

 somite stages. A drawing of the three somite stage was not 

 made, as the position of the germ cells here was almost identical 

 with their position in the primitive streak stage before somite 

 formation. Further description of this period of germ cell his- 

 tory is unnecessary. In the 4-mm. embryo, however, the germ 

 cells begin to leave the intestinal entoderm, as shown in figure 

 9a, Superficially, the 4-mm. embryo is characterized by the 

 acute cervical bend and prominent heart regions, but as yet 

 shows no external signs of limb buds. It is at this stage that 

 germ cells are first seen to be massing along the ventral wall of 

 the now-closed intestine. Certain it is that germ cells are still 

 to be seen in the lateral walls of the intestine, but their number 

 is small (observe fig. 9). It will be noted from this same figure 

 that a couple of germ cells are in the process of passing out of 

 the intestinal entoderm, while one cell is already visible within 

 ■ the loose surrounding mesenchyme, which shortly will go to 

 form a part of the permanent mesentery. .This is a critical 

 stage, and interesting because it so clearly presents the pass- 

 age of the germ cells from the entoderm into the mesoderm. 

 The next stage in my possession is the 5.5 mm. embryo which 

 externally shows well developed Umb-buds. The examination 

 of sections reveals the presence of germ cells in a well-developed 

 mesentery. What course is followed by the germ cells in reach- 

 ing this location cannot definitely be stated in the absence of an 

 intervening stage. However, with ones knowledge of the for- 

 mation of the mesentery it is not difficult to conceive of how this 

 might happen. It is probably not amiss to say that, as the 

 intestine continues to round up, the germ cells which have mi- 

 grated into the loose mesenchyme around the intestine pass up 

 and forward, through a process of growth and shifting of the 



