Mr F. E. Beddard on the Ovary of Echidna. 357 



malia, where the follicular epithelium surrounding the fully- 

 developed ova is always composed of a great number of 

 layers of cells, which form a specially dense accumulation in 

 tlie region of the ovum, the so-called discus proligerus, the 

 rest of the Graaffian follicle being filled with fluid. It is 

 only during the earlier stages of the development of the 

 ovum in the mammalian ovary that the follicular epithelium 

 consists of but a single layer of columnar cells. These facts 

 are well illustrated by several figures, which represent the 

 ova and portions of the ovary of OrnitliorliyncJius. 



The opportunity of carefully preserving the ovaries of 

 Echidna for histological study has been afforded me by the 

 recent death of a specimen in the Zoological Society's Gardens, 

 and I think it worth while to publish my results, since they 

 are, to some extent, fuller than those of Mr Poulton (who 

 had only comparatively poor materials to work at), though in 

 regard to the important fact relative to the structure of the 

 follicle I can only confirm the accuracy of his account. 



Mr Poulton's description of the ovary of Echidna is as 

 follows : " The condition of the ovaries of Echidna was such 

 that I could make out nothing except the important fact that 

 the follicular epithelium and zona pellucida are similar to 

 Ornithorhynchus" Although this sentence contains a correct 

 statement of two of the most important facts in the constitu- 

 tion of the ovum and follicular epithelium of Echidnct, the 

 matter appears to me to be worth going into in further 

 detail, and that I have attempted to do in the present paper. 



The epithelium covering the ovaries externally consists of 

 a single layer of columnar cells, the size of which is not 

 absolutely uniform over the whole organ ; in certain regions 

 the cells are considerably taller than in other regions. The 

 follicular epithelium of the ovarian follicles shows a greater 

 resemblance to the outer columnar epithelium of the ovary 

 in the character of the cells which form it ; and this fact is 

 not remarkable, since it is well known ^ that the follicular 



^ This is a point on which opinions differ. Dr Foulis believes that the 

 follicular epithelium is a derivation of the ovarian stroma. The most recent 

 edition of Quain's "Anatomy" (ninth edition) appears to favour the view 

 given in the text. 



