524 MR. F. E. BKDDAKD ON THE DEVELOPMENT AND [DeC. 7, 



filled with yolk-particles at the expense of their protoplasm must 

 tend to lose their activity for movement, their energy being spent in 

 the elaboration of yolk ; again, the thick layer of cells surrounding 

 the central cells would prevent any of the central cells from leaving 

 the interior of the follicle ; the result of further growth would 

 therefore necessarily lead either to the development of a number of 

 distinct ova remaining permanently within the follicle, or to the 

 excessive development of one of the cells, which would ultimately 

 form the ovum, or, finally, to the formation of a single ovum 

 out of the whole mass of cells. There are no facts which point to 

 the truth of either of the first two alternatives, while all the facts 

 at my disposal appear to prove the third alternative ; accordingly 

 the temporary fusion of the primitive ova in the Elasmobranch nest 

 and the degeneration of some of them becomes permanent in the 

 Dipnoi, the ovum being the equivalent of a whole " nest." Both Palae- 

 ontology and Anatomy point to the great age of the Dipnoi, which 

 may therefore easily be supposed to have retained ancient characters 

 in the structure of the ova, as they undoubtedly have in the structure 

 of the genital ducts. It is more generally believed that the Elasmo- 

 branchs are at a still lower level of organization ; if, however, as 

 Mr. Howes has pointed out to me, the Chimseroids are the 

 ancestors both of Elasmobranchs and Dipnoi, it may as easily be 

 supposed that the egg-nest of the former has been derived from the 

 egg-nest of the Dipnoi, as that the converse process lias taken place. 

 In this case the temporary fusion of primitive ova in the Sharks 

 and Rays is a reminiscence of their permanent fusion in Protopterus 

 and Ceratodus, It does not seem to me possible at present to say 

 which of these views is correct ; nor indeed can any comparison at 

 all of the two structures have any great weight until the structure 

 of the ovary has been thoroughly examined in such types as 

 Chimara and some of the more primitive Sharks. 



On the whole it appears to me possible to regard these remarkable 

 structures in the Dipnoi as corresponding to the egg-nests of other 

 Vertebrates ; but the apparent absence of any protoplasm in the 

 yolk-mass renders it extremely unlikely that the structure develops 

 into an embryo' ; on the other hand it is often very difficult, in an 

 ovum full of yolk, to distinguish the protoplasmic matrix ; it is 

 probable, however, that these structures do not undergo any further 



* I observed several ova undergoing degeneration— in one case belonging 

 to the type discussed here. The follicular epithelium was in a condition 

 of active degeneration, the cells becoming detached and passing into the inte- 

 rior of the ovum. (This process is not to be confounded with the nutrition 

 of the ovum by the follicular cells recorded iu this paper and in my last ; in 

 the latter case the follicular cells are large, crammed with yolk-particles, 

 and remain a continuous layer; in the degenerating ovum the folhcular cells 

 have decreased in size, contain little yolk, and great gaps are left by the disap- 

 pearance of tlie cells.) The yolk has also undergone great changes, the yolk- 

 spherules exhibit a vacuolated appearance and are of more irregular size, as if 

 8 number had become converted into fat-drops and had run together ; the 

 amount of yolk also was less, and the ovum in consequence was collapsed and 

 of irregular shape ; at several -points the walls of the ovum were altogether in- 

 distinguishable. The way in which the ovum degenerates does not in fact 



