INTRA-OVARIAN EGG OF SOME OSSEOUS FISHES. 63 



nuclear membrane as being of a distinct double contour and 

 well defined from the surrounding part, as well as from the 

 contents of the nucleus. I could cite many other authorities, 

 but it would lead me too far. 



III. The Egg-Membranes. 



At the recent meeting of the British Association at Bir- 

 mingham, I submitted a paper on the egg membranes of 

 osseous fishes. I pointed out that, in a section of the gur- 

 nard's egg, I had seen a thin membrane internally to the egg 

 capsule or " zona radiata," and that it had been already noticed 

 by Ransom and other observers. 



I think the egg-membranes constitute that part of the 

 Teleostean ovum on which most has been written. I shall 

 attempt to throw some light on the discrepancies which we 

 find among zoologists in regard to these membranes. All 

 zoologists agree as to the existence of one more or less thick 

 layer, which most of them believe to be pierced by minute 

 pores. Now I find that this layer has no less than seven 

 different names, as will be seen by the subjoined list : 



1. Zona radiata. — Balfour, Beneden, Brock, Mcintosh, Ovsiannikov, 



Reichert, Solger. 



2. Vitell. membr. — Aubert, Beddard (?), Cunningham, Haeckcl, Kolliker, 



Waldeyer. 



3. Egg-capsule. — His, Miiller, Prince. 



4. Yolk-sac. — Ransom. 



5. Zona pellucida. — Eimer. 



6. Chorion. — Leuckart, Rathke. 



7. Egg-shell. — Oellacher, Vogt. 



Leaving out the follicular layer, or " granulosa " as it has 

 been called especially by continental investigators, we have 

 besides the above-mentioned membrane, descriptions of one or 

 two or even three others. As I am here only dealing with the 

 intra-ovariau egg of a few marine forms, some of which were 

 not even ripe enough to possess egg- membranes, my observa- 

 tions will necessarily be somewhat incomplete in this respect. 

 I will commence with a description of the " zona radiata/' 



