OVARIES IN TELEOSTEAN AND ELASMOBRANCH FISHES. 187 



eg-gSj there are four.^ The outermost, in eggs about 'oS mm. 

 in diameter, is a very tliin, homogeneous, deeply staining 

 membi'ane, to which the follicular epithelial cells are closely 

 applied. It appears to me to answer to Eigenmann's 

 description of the outer membrane in Clupea vernal is. 

 Certainly, where this membrane is raised up from those 

 underlying it, "slender striations are seen to extend to the 

 zona radiata." The appearance and relative thickness of the 

 underlying membranes are shown in fig. 34. The second 

 outer membrane is by far the thickest in ovarian eggs at this 

 stage; it is roughly about three times as thick as the next 

 inner membrane. The zonoid layer [jy. v. I.) is present as 

 usual. 



The egg membranes in Zeus develop in succession from 

 without inwards. The fine homogeneous outer membrane is 

 formed first, but whether by the egg or by the follicular cells 

 could not be determined. The diffienlty of the determination 

 lies in the circumstance that the follicular epithelium is 

 present around the egg from a very early stage. Once the 

 outer membrane is formed, the others arise in succession from 

 the cortex of the egg. The manner in which they arise 

 from the cytoplasm of the egg was not followed with high 

 powers, but so far as could be made out each membrane at 

 its first appearance resembles the zonoid layer (p. r. I.), and is 

 later metamorphosed into a true zona. The definitive zonoid 

 layer is the last to form, and remains in the "living" 

 condition. It may, however, be regarded as a potential egg- 

 membrane. The regular radial arrangement of its proto- 

 plasmic fibrils, along which the nutrient secretion of the 

 follicular cells must pass, perhaps facilitates the equal and 

 symmetrical distribution of food material in the egg. 



Gathy's account (1900) of the mode of origin of the egg 

 membranes in Clepsine complanata appears to me to 



^ rultou (1898) mentions the tliick "double" capsule of the ovarian egs; 

 of Zeus, and adduces the condition as indicating the probable demersal cha- 

 racter of the ripe egg. Fulton does not appear to have noticed either the 

 extremely fine outermost membrane, or the zonoid layer. 



