524 MR. F. E, BEDDARD ON THE DEVELOPMENT AND [ Dec. 7, 
filled with yolk-particles at the expeuse 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 Pale- 
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 ata still lower level of organization; if, however, as 
Mr. Howes has pointed out to me, the Chimeroids 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 has 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 thorovghly examined in such types as 
Chimera 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 yoik, to distinguish the protoplasmic matrix; it is 
probable, however, that these structures do not undergo any further 
1 TI 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 in 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 follicular cells 
have decreased in size, contain little yolk, and great gaps are left by the disap- 
pearance of the cells.) The yolk has also undergone great changes, the yolk- 
spherules exhibit a vacuolated appearance and are of more irregular size, as if 
a number had become conyerted 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 oyum degenerates does not in fact 
