308 Origin and Migration of the Germ-Cells in Aeanthias 



Vol. I, Part 1, p. 125, of Quain's Anatomy contains a well-known 

 picture taken from Balfour and is designed to show this transformation 

 of epithelial cells into sex-cells and is labelled ^ Transverse section 

 through the ovary of an embryo shark showing the germ-epithelium 

 forming primitive ova." 



Later investigators in the embryology of this region in the dog-fish, 

 shark, etc., have also ascribed the origin of these cells to transformation 

 of the coelom epithelium, and have attempted to account for their pres- 

 ence in the unusual and distant positions. 



Euckert, 88, found the primitive ova in the segmental mesoderm of 

 Selachieme and made the observation that only a few of the cells of 

 this type lie outside in the unsegmented mesoderm, thus giving sup- 

 port to his belief in the Gonotome theory — that is, that the reproductive 

 organs of the vertebrates were originally segmented like the vertebrae 

 themselves. 



This use of the word Gonotome was called in question by Minot in 

 1894, in an article " Gegen das Gonotome," claiming that our knowledge 

 about these large cells was not sufficient to warrant us in believing 

 them to be necessarily all primitive ova since some were in positions 

 entirely outside the genital region. As we had no exact knowledge of 

 the origin, fate or meaning, they might even be ordinary cells in the 

 process of division. 



Carl Eabl, 96, believed these peculiar cells to be all primitive ova. 

 He found them first over a diffuse region lining the body cavity which 

 region subsequently became contracted. They were situated in both 

 the splanchnopleure and somatopleure, though most of them were in 

 the former. 



Like Balfour he could not explain their peculiar structure or the 

 granules of yolk in their protoplasm. He considered it difficult to 

 explain their disappearance from the somatopleure since there was no 

 certain evidence of their migration, and he also suggested the idea that 

 these more distant ones might be changed over into ordinary epithelial 

 cells. He did not hint at their presence before the formation of the 

 coelom. Thus the classical view is, that the germ-cells originate in the 

 ccelom epithelium. 



More recently, a few researches regarding the origin of the primitive 

 ova in a few more or less peculiar lower vertebrates show that in certain 

 forms at any rate these cells are differentiated very precociously even 

 before any embryo is formed and never arise from any somatic or body 

 cells. 



My own investigation on the origin of the primitive ova in Squalus 

 aeanthias or the common dog-fish, a typical elasmobranch. entirely dis- 



