OVARIES IN TELEOSTKAN AND ELASMOBIIANCH FISHES. 183 



date, and then tlie contraction of the yolk would not be 

 accompanied by the stretching of any filaments across the 

 space thus produced." 



Reasons will be given below for regarding this view as to 

 the origin of the zonoid layer as incorrect. 



Nutrition of the Egg by the Cells of the Follicular 

 Epitlielium. — It has been demonstrated in the case of 

 Talpa by Heape (1886), and in Echidna by Caldwell 

 (1887), that the zona pellucida is perforated by protoplasmic 

 processes connecting the protoplasm of the ovum with that 

 of the follicular epithelium. Eimer (1872) found the same 

 condition in the ovarian ova of reptiles. Balfour (1878), 

 although he observed that the cells of the follicular epi- 

 thelium in Raia and Scy Ilium, after being teased out in 

 osmic acid, had slender processes attached to them, was not 

 able to say that these had passed through the homogeneous 

 " vitelline membrane." In the ovarian ova of Teleosteans 

 Fulton (1898) thinks that the existence of radial pores in the 

 zona is unproved. 



Eigenmann (1890), on the other hand, considers that their 

 presence is well authenticated. He saj^s, "The meaning of 

 the pore canals in the intra-ovarian egg", at least, needs little 

 discussion. In most of the sections prepared, where the 

 granulosa cells are slightly raised from the zona radiata, 

 processes of the granulosa cells can be seen to enter the pore 

 canals." So far as I know, neither in teleostean nor in 

 elasmobranch fishes have processes of the follicular cells 

 been seen actually to traverse the substance of the egg 

 membrane. In Chim^era, however, they can be clearly seen 

 to do so (fig. 30). 



Gegenbaur, Balfour (1878), Yan Beneden (1880), and 

 others were of the opinion that the deutoplasm is manu- 

 factured by the egg itself, and is not derived from the cells 

 of the follicular epithelium. This is proved by the following- 

 facts — which hold, at any rate, for Teleosteans and Elasmo- 

 branchs : — (1) The yolk particles are first formed at some 

 distance in from the surface of the egg. The cortical layer 



