BEPRODUOTIVE ELEMENTS IN MYXINE ULUTINOSA. 67 



separated from the epithelium, into continuity with proto- 

 plasmic fibrils outside the membrane. These fibrils I believe 

 to be in the natural condition continuous with the cells of the 

 epithelium, and I conclude that the striae are really pores in 

 the membrane, which are filled up by protoplasmic processes 

 from the cells of the follicular epithelium. A similar condition 

 of things exists, and has been described by many authors in 

 Teleostean ova, and has been very completely elucidated by 

 Owsyannikow in the paper already cited. Owsyannikow ob- 

 tained his most satisfactory results from examination of the 

 eggofPerca fluviatilis. In this species the vitelline mem- 

 brane consists of two layers, both of which contain pores, and 

 are therefore called by him zona radiata externa and in- 

 terna. The zona externa is in the ripe ovum gelatinous, 

 and causes the adhesiveness of the egg membrane. I have 

 myself examined sections of the vitelline membrane of the 

 ovum of the cod after deposition. The pores here are quite 

 straight and never branched, and they are somewhat further 

 apart than those in the egg of Myxine. In the cod I could 

 discover no separation of the membrane into two layers. It 

 seems evident to me that the vitelline membrane in the ovum 

 of Myxine, which is a zona radiata in the usual sense of the 

 term, is homologous with the zona radiata in Teleostean 

 ova. When there are two zonae radiatae, as in Perca 

 fluviatilis and Osmerus eperlanus, according to Ows- 

 gannikow, these seem to be simply parts of one membrane 

 diflPerentiated in physical properties, but essentially similar in 

 structure. Balfour regards the zona radiata in vertebrate 

 ova as a diflFerentiation of the outermost layer of the yolk. It 

 seems to me much more probable that it is produced by the folli- 

 cular epithelium. It is concluded by most authorities that the 

 pores in the zona radiata are occupied by processes from the 

 cells of the follicular epithelium, and that the function of these 

 processes is to convey nutriment to the ovum. In Myxine such 

 processes exist. The manner in which the membrane arises I 

 conclude is as follows : — The deeper part of the elongated epi- 

 thelium cells is gradually changed into the zona radiata, the 



