5/8 THE STRUCTURE AND DEVELOPMENT 



spond with those in Elasmobranchs appears to me clear' from 

 Eimer's figures, but I have not myself studied any Reptilian 

 ovum. My reasons for dissenting from both Semper's and 

 Schultz's views on the nature of the two forms of follicular cells 

 have already been stated. 



The Vitellus and the development of the yolk spherules. 

 Leydig, Gegenbaur, and Schultz, have recorded important ob- 

 servations on this head. Leydig 1 chiefly describes the peculiar 

 characters of the yolk spherules. 



Gegenbaur 2 finds in the youngest eggs fine granules, which 

 subsequently develop into vesicles, in the interior of which the 

 solid oval spheres, so characteristic of Elasmobranchs, are de- 

 veloped. 



Schultz describes in the youngest ova of Torpedo the minute 

 yolk spherules arranged in a semi-lunar form around the ec- 

 centric germinal vesicle. In older ova they spread through the 

 whole. He also gives a description of their arrangement in the 

 ripe ovum. Dr Schultz further finds in the body of the ovum 

 peculiar protoplastic striae, arranged as a series of pyramids, 

 with the bases directed outwards. In the periphery of the ovum 

 a protoplastic network is also present, which is continuous with 

 the above-mentioned pyramidal structures. 



My observations do not very greatly extend those of Gegen- 

 baur and Schultz with reference to the development of the yolk, 

 and closely agree with what Gegenbaur has given in the paper 

 above quoted more fully for Aves and Reptilia than for Elasmo- 

 branchii. 



In very young ova the body of the ovum is simply granular, 

 but when it has reached about O'5 mm. the granules are seen to be 

 arranged in a kind of network, or spongework (PL 25, fig. 21), 

 already spoken of in my monograph on Elasmobranch Fishes. 



This network becomes more distinct in succeeding stages, 

 especially in chromic acid specimens (PL 25, fig. 22), probably 

 in part owing to a granular precipitation of the protoplasm. In 



Witrzburg, Bd. iv. He says, in reference to the flask-shaped cell, p. 166, " Hochstens 

 wiirde ich die P'unktion der grossen Follikelzellen als eiuzellige Driisen mehr be- 

 tonen." 



1 Loc. cit. ' 2 Loc. cit. 



