5£_ 



female, one male. In the two former the totals were 136 and 127, 

 in the latter 137. 



From these observations it is concluded, that the number of pri- 

 mary germ-cells in Pristiurus is alike for both sexes, and that 2" here 

 is 128, the actual number of primary germ -cells, destined to enter 

 the embryonic body, being 2ii— l, or 127. 



In every single one of the embryos, apart from those 

 encountered upon the mesentery or splanchnopleure, 

 abnormally situated primary germ-cells obtain. The 

 number of these again varies, being 49 in one of the younger embryos, 

 and only 3 in one of the older ones. The total number of such aber- 

 rant germ-cells, tabulated in my notes under the heading "found else- 

 where", is 180, or an average of about 14 for every embryo, or nearly 

 11 "lo- Under this heading only primary germ-cells in utterly impos- 

 sible situations are included. Were one to embrace within it many 

 of those met with pretty low down upon the splanchnopleure — which 

 in Raja, as unpublished observations show, usually degenerate — the 

 percentage would be considerably higher. 



Of the germ-cells found elsewhere a common situation, especially 

 in the older embryos, is the body -cavity. Here in almost every em- 

 bryo careful search reveals the presence of a few such, and frequently 

 they are in degeneration. The terminal portion of the body -cavity 

 is the usual situation, but occasionally one or two may be found in 

 other parts of it, or even near its anterior end. Some may lie some- 

 where or other in the somatopleure, as Rabl has noted, but their 

 number is not great, at any rate in older embryos. They may be 

 below the gut in the tissues of the mesoblast or mesenchyme, within 

 the gut-epithelium, in the liver, or underneath the epiblast. Here, 

 as in Raja, a common position is upon the subintestinal vein. In this 

 situation some are encountered in practically every embryo. Thus, in 

 embryo no. 19 of the three "found elsewhere" one was free in the 

 body-cavity, one lay in the liver, and the remaining one was applied 

 to the subintestinal vein. 



In Pristiurus no specially close search has been made for them 

 in the nervous system or head, but in one embryo a single vagrant 

 germ-cell was seen in the gill -region, and in another a solitary in- 

 stance in the pericardium. Sometimes, especially in the younger em- 

 bryos, they are encountered somewhere or other within the blastoderm 

 outside of the embryo, or upon the epiblast or mesoblast of the yolk- 

 stalk, connecting the embryo with the yolk-sac. Within the mesentery 

 of Pristiurus the number of germ-cells is never very great: upon the 



