_58_ 



From the sizes of the fresh blastoderms of Pristiurus, as given 

 by llüCKEKT ('99), from those of the primary germ -cells in various 

 embryos, and, lastly, from those of the products of the latest cleavage, 

 it has been calculated, that as in Micrometrus (Eigenmann), Cyclops 

 (Haeckek), and Raja, the primary germ-cells go back to the cleavage, 

 to one of the products of this as the primitive germ-cell. 



Prior to the present researches those of Rabl^) are the most 

 recent ones upon the germ-cells of Elasmobranchs, and the form spe- 

 cially dealt with by him was Pristiurus melanostomus. His embryos 

 and those described here of this species were obtained from the like 

 source, the Zoological Station of Naples. 



Before writing about the germ-cells of Raja, the writer had more 

 than once read through Rabl's work. It is referred to several times 

 in the previous publication; but, as I now recognise with regret, the 

 references may appear to be somewhat scanty. In addition to noting 

 his record of germ -cells in the myotomes and nephridial tubules, it 

 should have been stated, that he had found them in the splanchno- 

 pleure, some in the somatopleure, and even in one case in the cutis- 

 lamella of a myotome. These finds were overlooked, when writing my 

 own paper in consequence of further statements of his on p. 754 — 755. 

 The more important of these I now proceed to summarise, merely 

 adding, that the whole of his account should be read. 



According to Rabl, the germ-cells appear very early in the de- 

 velopment, long before any other part of the urinogenital system. So 

 early is this, as my observations have taught me, that they precede 

 the formation of any trace of an embryo. He states, that they are 

 found from the beginning in that region of the body, in which we 

 later on meet with them, that they never appear in front of the pro- 

 nephros, and that they do not extend back much beyond the point, 

 where in older embryos the hinder end of the germinal fold occurs. 

 "Ab und zu können wohl versprengte Keime an ganz abnormen Stellen 

 vorkommen'-^), an Stellen, die nicht die geringste Beziehung zur Ent- 

 wickelung der Geschlechtsdrüsen zeigen ; aber solche Fälle sind seltene 

 Ausnahmen, sie sind als Ausnahmen sofort und mit Sicherheit zu er- 

 kennen und sie erschüttern die Regel nicht. Der pathologische Anatom 

 mag solchen thatsächlich nachweisbaren , versprengten Keimen eine 



1) C. Rabl, Theorie des Mesoderms. VI. Ueber die erste Ent- 

 wicklung der Keimdrüse. Morphol. Jahrb., Bd. 24, 1896, p. 747 — 756. 



2) From Rabl's work one does not gather, that he has himself 

 noted many such "vagrant germs". 



