GERM CELLS IN TATUSIA NOVEMCINCTA 353 



tissues, and also through their independent amoeboid move- 

 ment into the forming mesentery. The germinal epithelium is 

 present on either side of the mesentery (fig. 10a), but as yet no 

 thickening has occurred to form the lateral ridge. The germ 

 cells at this time are found in equal numbers in three places. 

 They can be seen located between the blood vessels of the mesen- 

 tery as seen in (fig. 106), but are never found at this time in. the 

 mesentery below the level of these vessels. The germ cells may 

 also be found at the angle of the mesentery and the germinal 

 epithelium (fig. 10). The cell seen in figure 10 is unusually 

 large and therefore not quite typical. A number of germ cells 

 seem to pass dorsal, above the root of the mesentery and of the 

 region of the germinal epithelium, into the loose mesenchyme 

 beneath the aorta. Strangely enough, at this period the cells 

 are not particularly amoeboid in shape (fig. 10). It is notice- 

 able, also, that they are larger than usual. In addition, the 

 nucleus instead of being granular has become more or less reticu- 

 lar in appearance. While the germ cells are traveling into the 

 germinal epithelium, the latter thickens and germ cells become 

 embedded in it. The germ cells .are very easily distinguished 

 from the peritoneal cells among which they lie (fig. 11), so that 

 it is impossible to believe that they could ever be derived from 

 these cells. 



By the time the embryo is 10 mm. long, the germ cells have 

 ail migrated into the well-developed indifferent gonad (fig. 11). 

 At this time as seen from the drawing they are very conspicuous 

 for their size. The apparent increase in size is due, no doubt, 

 to the fact that the cells are preparing for division. 



DISCUSSION 



The migration of the germ cells froni the entoderm to the sex 

 anlage is unmistakable. Throughout, the germ cells can easily 

 be followed. But the question as to the origin of these same 

 cells remains somewhat doubtful, although the writer is of the 

 opinion that the conclusions reached in this paper are of rather a 

 convincing nature. The examination of stages now at hand has 



