OVARY AND INTRA-OVABIAN EGG IN TELEOSTBANS. 307 



the forming ovaj and ultimately form the follicle. I find no sign of 

 a central cell in the nest, enlarging at the expense of the others, 

 becoming itself the ovum while the rest form the follicle. These 

 nests of epithelial cells which become ova have a singular resem- 

 blance to the nests described by Balfour (loc. cit.) for Elasmo- 

 branchs. In his description of the formation of the permanent ova 

 several primitive ova coalesce to form nests, masses, or syncytii. 

 These nests enlarge in size as development proceeds — explained by 

 the probable division of nuclei without a corresponding division of 

 the protoplasmic matrix, so that nuclei become very numerous. 

 Some of the nuclei unite and become the nuclei of permanent ova, 

 and are budded off with their surrounding protoplasm, which is of 

 small amount ; others again break up, and are used as pabulum for 

 the young ova. " In many cases normal nuclei of the germinal 

 epithelium may be observed within the ovum.^' The ova then 

 become surrounded by germinal epithelium, from which the follicle 

 is formed. If in the common dab we call the epithelial cells 

 primitive ova, the analogy is practically complete. 



My study of the egg membranes themselves is of course confined 

 strictly to those of intra-ovarian ova. I may preface the few state- 

 ments I have to make by explaining that I accept the term " zona 

 radiata " as used by Balfour and some others in describing the con- 

 stant and most important membrane, and find it convenient to 

 treat of other membranes as inside or outside, according to their 

 position with regard to that membrane. What I shall call the zona 

 radiata is, therefore, the vitelline membrane of Waldeyer, KoUiker, 

 and others ; the egg capsule of His and Miiller ; and the zona pel- 

 lucida of Eimer. 



Cunningham (13) describes the almost ripe ovum in the sole when 

 the radial stride are very distinct. The vitelline membrane (zona 

 radiata) described by him is considered to be the only membrane 

 present. My examination of soles' ova inclines me to the conclu- 

 sion that there is a membrane inside the zona radiata, as well as 

 the follicular layer outside. The membrane is seen to best 

 advantage in eggs in which some slight shrinkage of the protoplasm 

 has taken place, and fig. 10 represents the appearance as seen in an 

 egg of this description. Scharff figures an exactly similar condi- 

 tion in the egg of Trigla, and other authors have also described it. 

 Kupffer, when treating on the herring, compared this structure to 

 the true vitelline membrane. Ransom calls it the inner yolk-sac — 

 his outer yolk-sac being the zona radiata of Balfour. On the other 

 hand. His, Waldeyer, and Brock deny its existence. 



The membrane may be the product of the vitellus, or it may be 

 derived from the zona radiata, and it is also possible that the zona 



