MIGRATION OF GERM CELLS IN AMIURUS NEBULOSUS. 359 



In number 4, one cell was in the entoderm, and in number 6, 

 a germ cell was between the yolk and the mesoderm. 



EMBRYOS 5 MM. LONG. 



The coelomic cavity is completely formed. With the growth 

 in length a greater differentiation in tissues has been going on. 

 The germ cells are found in the region of the hind gut, the ma- 

 jority of them are posterior to where the tail leaves the yolk. 

 The most anterior cells are 0.080 to 0.220 mm. anterior to this 

 region. The most posterior cells were 0.180 to 0.290 mm. 

 anterior to the anus. With few exceptions the germ cells 

 were found in the splanchnopleure (Fig. 3). In one embryo a 

 nest of four cells was found in the somatopleure (Fig. 4) . In the 

 same embryo a germ cell was found lying in the center of the cavity 

 between the somatopleure and the ectoderm. This was such 

 an unusual position that it seems reasonable to think that it 

 might have been torn away from the somatopleure in sectioning; 

 however, the section has not the appearance of having been torn 

 in any way. The size and appearance of the germ cells of em- 

 bryos 5 mm. long are the same as in the preceding stage, but they 

 are much more conspicuous due to the greater differentiation of 

 the surrounding mesoderm. The cells are in the dorsal half of 

 the splanchnopleure and often give the appearance of crowding 

 toward the mesentery next to the alimentary tract (Fig. 5). 

 The germ cells are distributed throughout a distance averaging 

 0.420 mm. in length. The following table shows in three embryos 

 the unsymmetrical arrangement, the number of cells, the length 

 of region throughout which the germ cells are distributed, the 

 distance anterior to the anus of the most posterior germ cell and 

 the distance anterior to the region where the tail leaves the yolk 



of the most anterior germ cell. In embryo number 2, 2 germ 

 cells were in the mesentery; 6 cells were in the mesentery in 

 number 3. 



