308 OVARY AND INTRA-OVARIAN EGG IN TELEOSTEANS. .• 



may be derived from it. The ready way in wMcli it seems, by 

 clinging to the yolk mass, to separate from the zona radiata, appears 

 to favour the idea that it has no immediate relation with the latter. 

 In this case it may be possible that, in those species in which the 

 membrane is present, no pabulum can be supplied to the ovum from 

 the follicular layer through the supposed radial pores. I cannot 

 prove the origin of this structure, and therefore hesitate to give it 

 the name of vitelline membrane. It has a very distinct double 

 contour, and appears to be proof against stain. 



What becomes of it when the ovum is shed and comes in contact 

 with the water I am, unfortunately, unable to say. Its relation to 

 the perivitelline space would be a point of some interest ; and 

 further, if this space contains albumen, as stated some time ago by 

 Raffaele, and not water which has gained access through the micro- 

 pyle or radial canals, a somewhat important function might be 

 found for it. 



In none of my sections do I find a membrane outside of the 

 zona radiata. The follicular layer is often irregular in its composi- 

 tion, and sometimes cloudy in appearance, and a distinction between it 

 and any outer layer of the zona radiata, therefore, would be difficult. 

 I am inclined to think, however, that an outside membrane of this 

 kind must occur in very few species (14). Brook (15) describes a 

 vitelline membrane outside of the zone radiata in Trachinus vipera, 

 and Balfour (16) notes one in the herring and describes an imper- 

 fect one in the perch, but so far as I know these ai"e the only 

 instances. 



IV. The Ovary. 



In treating of the whole organ I do not intend that my remarks 

 should apply to the ovaries which, according to Jules MacLeod (17), 

 constitute " la premiere forme '' — the ovaries of Salmonidse and 

 Mursenidae, where the ova are dropped into the abdominal cavity, 

 and find their way to the exterior by abdominal pores. In the case 

 of these fishes the arrangement of the ovary is, to a certain extent, 

 reversed, the germinal epithelium being free, and not enclosed, so 

 as to form a tube, by a surrounding membrane. 



Although I have described the nucleoli of the conger's egg, I 

 shall therefore not touch on its ovary, but must refer the reader to 

 the account given by Cunningham (18). I shall confine my remarks 

 to the ovaries of those fishes in which the epithelium is enclosed 

 by a surrounding membrane, and the eggs, becoming free in the 

 centre of the organ, are extruded through an oviduct. 



The ovary is usually described as a tubular structure, and in the 



