284 MR. F. E. BEDDARD ON THE [ May 4, 
body 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 cvum 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 Scyl/ium, 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 (/oc. 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 
which 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 His, 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 for their demonstra- 
tion; in these 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 (pl. ii. figs. 22, 23) is very 
1 « Hierstock der Knochenfische,’ p. 22, &e. 
2 “Studien tiber das Ei, hauptsachlich bei Knochenfischen,” Mém. d. l’Acad, 
d. St. Pétersh. t. xxiii. no. 4. 
