373 

 5. The ovarian ovum of Lepidosiren (Protopterus). 



By Frank E. B eddard, M.A. Prosector to the Zoological Society of London. 



eingeg. 19. April 1886. 



Some incidental observations on the structure of the ovary 

 and ova of Ceratodus and Lepidosiren are to be found in a recent 

 memoir on the visceral anatomy of these two genera by Dr. Howard 

 A y er s ^ There are several figures of ova given in the plates and the 

 author remarks that structurally the ovary ressembles the same organ in 

 the Amphibia ; there is however no detailed description of the origin 

 and maturation of the ovarian ova. Having had the opportunity 

 of preserving the viscera of a specimen of the African Ijepidosiren 

 [Protopterus) which lived for some months in the Zoological Society's 

 Gardens, I have been able to study the ova; the following notes are 

 upon the more interesting results arrived at. 



In ova of the first stage the contents of the ovum were almost uni- 

 formly protoplasmic ; there was hardly any appearance of yolk forma- 

 tion; the peripheral region in the larger ova was hardened into a 

 distinct membrane radiately striate. The follicular epithelium surroun- 

 ding the ova is composed of a single layer of flattened, nucleated cells. 

 The germinal vesicle is large -with numerous minute nucleoli ranged 

 round its periphery. 



In the next stage the follicular epithelium has undergone a re- 

 markable change ; the cells from being comparatively small and flatte- 

 ned have increased enormously in size, and rest directly upon the yolk, 

 which now occupies the whole extent of the ovum. There is no trace 

 of any membrane dividing the ovum from its follicular cells ; in certain 

 cases even the boundaries of the latter were indistinguishable and their 

 nuclei alone were visible forming a peripheral layer round the ovum ; 

 these appearances may represent the real state of aflairs, but as the 

 limiting membrane of the follicular cells was obvious enough in other 

 specimens it is more probable that they are due to defective prepara- 

 tion. In the connective tissue sheath which surrounds the follicle were 

 numerous blood capillaries gorged with blood ; these capillaries Avere 

 pressed down among the follicular cells and are evidently hypertro- 

 phied in relation to the formation of the yolk going on in the sub- 

 stance of the ovum. The follicular cells were filled with 

 small round highly refracting bodies which are indistin- 

 guishable from the yolk spherules filling the ovum. In the 

 interior of the ovum as already remarked were innumerable yolk par- 

 ticles of small size which were spread uniformly throughout it there 

 being no distinction between the peripheral and central regions; 



1 Jenaische Zeitschr. 1885. p. 479. 



