59 



pathogenetische Bedeutung- beimessen, und sie mit der Entstehung von 

 Geschwülsten und Mißbiklungeu in Beziehung bringen ; aber man wird 

 dabei stets im Auge zu behalten haben, daß wir irgend eine verläß- 

 liche Kenntnis über das weitere Schicksal solcher Keime nicht be- 

 sitzen." 



While placing restrictions upon their longitudinal extension, he 

 grants them a very wide transverse distribution. How wide is not 

 defined, and probably Rabl would at that time have refused to re- 

 cognise their possible occurrence in, e. g., the nervous system, or hypo- 

 blast, or body-cavity. In Pristiurus I have not found very many va- 

 grant germ -cells in front of the pronephros, but in no. 13 (5 mm) 

 there are 6, and in no. 12 (5,5 mm) 3 in front of this region. And, 

 while they are usually most thickly grouped in or about the site of 

 the future "sexual gland", they may and at certain periods (i. e., in 

 almost all of the embryos previously described), some few usually are, 

 to be found nearly as far back as the body-cavity extends. 



He writes further on, that it is difficult to say what becomes of 

 those upon the somatopleure and in the myotomes. For Raja, at any 

 rate, this difficulty can be removed. In certain older embryos evidences 

 have now been gleaned of the atrophy and degeneration of large num- 

 bers of germ-cells upon the splanchnopleure, where they are abundant, 

 and even upon the somatopleure, where, as Rabl also notes, they 

 are rarer. 



Recalling Balfour's idea, that at certain periods they might be 

 capable of amoeboid wanderings, he states, that he has been unable 

 to find any certain evidence of this. In Pristiurus the failure is hardly 

 remarkable, for it is not a very favourable form, in which to obtain 

 such, not for a moment comparable to Raja batis, and probably the 

 methods of staining, employed by Rabl, were at fault ^). How far the 

 wanderings of the germ-cells in Pristiurus can be established has al- 

 ready been seen in the account of the younger embryos. 



Of Rabl's suggestions concerning the germ - cells the one lacking 

 even the least basis of fact is, that possibly the aberrant germ - cells 

 of the somatopleure etc. may later on be converted into — epithelial 

 cells! This idea, however, is only in too complete accord with the 

 doctrines of current embryology. Often in their degeneration germ- 



1) It would be a very easy matter to stain an early skate-embryo 

 in such a way, that, while it was apparently exquisitely prepared for 

 observation, even a skilled embryologist might be unable to find any 

 germ-cells in unusual places. Then stain it differently, and another 

 picture is the result. 



