1886. | STRUCTURE OF THE OVUM IN THE DIPNOI. 525 
changes, though the degeneration of a few out of an immense number 
(see footnote) is hardly proof of this. IfI were in a position to deny 
the presence of a germinal vesicle, the absence of this essential element 
in the ovum would be evidence of some force in the same direction. 
On the other hand, the energy showed by the central cells and the 
cells of the follicular epithelium would be entirely thrown away in 
this case ; and it is very difficult to imagine the continuance of such 
a wasteful process in the ovary—the organ chiefly concerned with 
the preservation of the race’. 
A formation of ova in the Vertebrata by a fusion of cells has been 
stated to exist, but has been subsequently denied. 
Goette’s observations on the formation of the ovum in Bomdi- 
nator”, referred to in my former paper, have been explained away by 
Nussbaum *, who considers that the polynuclear condition described 
by Goette is the result of the proliferation of the nucleus of a 
primitive germinal ceil, and is not produced by the approximation 
of the nuclei of a number of distinct cells which subsequently are 
fused. 
The observations of v. Siebold* are of interest in relation to this 
question. 
In Apus the ova are formed in spherical acini which containa number 
of cells of which one grows at the expense of the rest. This cell 
finally comes to occupy the whole of the interior of its acinus, the 
remaining cells dwindling indefinitely ; the nucleus disappears, and 
yolk-formation sets in. When the cell has been, for the most part, con- 
verted into yolk it moves down the duct which connects the acinus with 
one of the branching tubes of the ovary, and there fuses with one or more 
cells which have been produced in other acini by a similar course of 
development. The fused mass becomes surrounded by a membrane, 
and is the ovum. In my preliminary notice in the ‘ Zoologischer 
Anzeiger’ I have referred to the observations of v. Siebold, and 
differ very widely from a description (Arch. fiir mikr. Anat. 1886) of the 
degenerating ovum of the trout. 
I may also take this opportunity of referring to an ovum of Ceratodus in a 
similar condition of degeneration. I erroneously mentioned this ovum (Zool. 
Anzeig. No. 236) as a nearly fully mature ovum belonging to the multicellular 
or plasmodial type; it may very likely belong to this type, but the appear- 
ances which it presents are indicative of degeneration, and not of maturation. 
The follicular epithelium is not separated by any membrane from the contents 
cf the ovum (fig. 2); its cells in a few cases are loaded with brown pigment, and 
many of them haye migrated into the ovum, the contents of which have been 
largely absorbed, probably by these cells; in consequence of this the ovum is 
collapsed. 
I have noticed a similar state of affairsin the ovary of a newt (Molge waltiii), 
which I purpose to describe on some future occasion. 
1 Tt has been suggested to me, in conversation, by Prof. Lankester that 
these structures may serve as food for the embryos, being deposited along with 
the ova, or that they may be reservoirs of nutritive material aiding in the 
growth of the intra-ovarian ova. Wither of these suggestions appears to me 
to be extremely plausible. 
? Arch. f. mikr. Anat. Bd. xviii. 
* Entwickelungsgeschichte der Unke. 
* Beitrige zur Parthenogenese der Arthropoden. Leipsic, 1871. 
