284 MR. F. E. BEDDARD ON THE [May 4, 



Ijofly of the ovum ; this membrane does not appear until after the 

 yolk has begun to be formed. 



Leaving the question as to the origin of these ova undecided for 

 the present, the penetration of the follicular epithelium into the 

 interior of the ovum and the formation of yolk by the follicular cells 

 are in my opinion strongly supported by the facts that I have been 

 able to bring forward. I will now compare these facts with similar 

 observations on other ova. 



A migration of follicular cells into the ovum has been recorded by 

 several writers, but other writers have thrown doubts upon the 

 accuracy of these observations. 



In Elasmobranchs and Amphibia nothing of the kind has been 

 recorded ; Balfour, in studying the ovarian ova of 5'c7///?M»n, particularly 

 directed his attention to this point, but was unable to find any 

 trace whatsoever of cells such as have been described by His in the 

 Teleostean ovum ; he suggests indeed that His may have 

 mistaken the white yolk-spherules for such cells ; the resemblance 

 of white yolk-spherules to cells is not a little striking, and may easily 

 have led to mistakes. 



With regard to the Teleosteans, however, there is some variety of 

 opinion as to this point. His ' has described a migration of the 

 follicular cells through the pores of the zona radiata into the interior 

 of the ovum ; but Brock {loc. cit. p. 558) doubts the truth of this 

 observation, not merely because he did not himself succeed in seeing 

 any such migration, but because it appeared to him inexplicable 

 that if there were so general an immigration the follicular epithelium 

 should yet maintain its continuity. 



The most recent writer on the subject whose memoir is known 

 to me is Owsjannikow ^. This author describes in detail a 

 number of facts relative to the structure of the Teleostean ovum 

 Avhich are often somewhat difficult to understand. With regard to 

 the supposed immigration of cells (leucocytes) into the interior of the 

 ovum, believed by His to occur, this author states that it has 

 not been observed by him, and that further the necessity for such a 

 process of nutrition does not exist, since nutritive material is supplied 

 to the ovum through the processes of the follicular cells, which are so 

 universally admitted to pass through the egg-membrane. At the 

 same time Owsjannikow describes in Osmerus and Acerina a peculiar 

 condition of the yolk, also referred to by Uis, but denied by others, 

 which in a certain degree is similar to the condition which I have 

 described in the present paper in Lepidosiren. The yolk-bodies 

 ("Dotter-Kugeln ") contained in many cases nuclei often difficult to 

 show and needing most complicated processes fur tlieir demonstra- 

 tion ; in tliese structures, which the author calls cells, the oil-drops 

 take their origin. Without additional investigations it does not 

 seem to me permissible to regard these bodies as true cells ; their 

 appearance in Owsjannikow's figures (pi. ii. figs. 22, 23) is very 



' ' Eierstock der Knocheufische,' p. 22, itc. 



^ "Studien iiber das Ei, liaiijitsacblich bei Knoelienflsclien," Mem. i\. I'Ai^ad. 

 rl.,fc. PetPrsb. t. xxxiii. no. 4. 



