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Show 284 MR. F. E. BEDDARD ON THE [Ma v 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 tor 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 m y 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 Scyllium, 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 Owsjannikow2. 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 demonstration ; 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 (pi. ii. figs. 22, 23) is very 1 ' Eierstock der Knochenfische,' p. 22, &c. a " Studien liber das Ei, hauptsachlich bei Knochenfischen," Mem. d. TAcad, d. St. Petersb. t. xxxiii, no. 4. |