56_ 



meration no attempt was made to distinguish those ou the mesentery 

 from those in the normal position; for, owing to the non-diflerentiation 

 of the germinal nidus, such a distinction could not be carried out. 

 In this embryo there were many germ- cells in the "gono-nephrotome". 



Pristiurus no. 6 is about 4 mm, 40 somites were counted. An 

 enumeration of the normally placed germ-cells was not attempted, but 

 little more than half the full number can be in this position , for at 

 least 60 vagrant germ-cells were noted. Some were still in the blasto- 

 derm, 12 being noted here, others lay between epiblast and somato- 

 pleure, others again under the epiblast, one was in the body -cavity, 

 one in the gut-cavity, three in the hypoblast, several low down upon 

 the splanchnopleure, two on the somatopleure, eleven under the epi- 

 blast, and two only in the germinal path between gut and splanchno- 

 pleure: and three of them were of larger size than usual, i. e., mega- 

 spheres. 



Pristiurus no. 4, whose size and external characters were not 

 noted, probably measures about 2 mm, and there cannot be many 

 more than 20 somites present. The embryo is, therefore, very little 

 older than the youngest, in which Rabl found germ- cells. The germ- 

 cells in embryo no. 4 have not been counted. Owing to their number 

 and the small size of the embryo their enumeration would be a very 

 difficult task, even for one, who had had much experience of such 

 work. All the embryonic cells still contain yolk, but this is never in 

 any case as much as that within a germ -cell. There are no germ- 

 cells within the head, apart from one solitary example beneath the 

 epiblast of the gill-region. For some distance behind the site of the 

 future pronephros the number of germ -cells is not large. Two are 

 noted under the epiblast almost outside the embryonic foundation, 

 there is one in the splanchnopleure, followed by two or three others, 

 then one in the unsplit mesoblast almost outside the embryonic body, 

 and a couple rather low down on the future splanchnopleure and to 

 its inner side. There is here no body-cavity, even within the embryo. 

 Further on another is encountered in the mesoblast just where em- 

 bryo and yolk-sac meet, and, finally, there are a few others in the 

 unsplit mesoblast at about the site of the future germinal nidus. 



In the following row of sections they come in shoals. Here one 

 encounters them not only in the site of the future germinal nidus, but 

 also lower down, several even in a section, along the side of the future 

 splanchnopleure, the mesoblast being as yet unsplit. Then there is a 

 single one under the hypoblast of the top of the yolk, followed by 

 one in the gut-epithelium. They now lie nearly all along the un- 



