The germ-cells. 633 



It is not unknown, that germ-cells may occur in places other than 

 the germinal nidus. Balfour ('78, p. 131) was the first to record 

 their presence "outside the segmental ducts and segmental tubes", and, 

 occasionally, "in a part of the mesoblast, which distinctly belongs to 

 the body-wall". Later a portion of them was described by Rückert 

 ('88) as lying within the myotomes, and more particularly within that 

 portion of the segmented mesoblast, to which he applied the term 

 nephrotome. 



Hoffmann and Prenant also describe them in abnormal positions. 



More recently, Rückert's finds have been commented upon and 

 confirmed by Rabl ('96), without any definition of a wider extension 

 of their occurrence. Indeed, the latter author is inclined to minimise 

 the abnormalities found. He admits (p. 754), that now and again 

 "versprengte Keime" may be met with in quite abnormal situations, 

 which have not the remotest connection with the development of the 

 sexual organs. He admits this, but one does not gather from his 

 description, that he has noted any such instances. Moreover, he states 

 that such cases are rare exceptions, as such immediately recognisable, 

 and "sie erschüttern die Regel nicht". 



Rabl's homily is directed against the pathologists, who are dis- 

 posed — and, as will be seen, rightly so — to attach very great and 

 grave importance to such "lost germs". 



The tables already given sufficiently emphasize the wide diver- 

 gence between Rabl's finds in Pristiurus and my own in Raja. 

 Without for a moment suggesting, that the percentage of abnormally 

 placed or "lost germ-cells" may be as high, or anything like as high, 

 in Pristiurus as in Raja hatis., I must none the less be permitted to 

 express my doubts as to the validity of Rabl's sanguine conclusions. 

 Stain an embryo with carmine or haematoxylin in the ordinary ways, 

 and it becomes a difficult matter to find "lost germ-cells". At any 

 rate, they are then easily overlooked. Treat the same embryo with 

 Heidenhain's haematoxylin, and a very different picture of affairs is 

 the result. 



The writer had studied skate-embryos for years, before any con- 

 siderable number of "lost germ-cells" arrested his attention. Moreover 

 in Scyllium canicula^ a form closely allied to Pristiurus, such "lost 

 germ-cells" do occur; though, so far as I have yet seen, they are not 

 as numerous as in Raja ^). 



1) Pristiurus is no exception. In /Sc^/Z^mm-embryos they have been 



