1886. ] STRUCTURE OF THE OVUM IN THE DIPNOI. 524 
affected by the borax carmine, and is throughout of a similar struc- 
ture; there is no structure resembling a nucleus to be seen. This 
central mass is clearly a further development of the condition 
described in the second stage. 
In one example, displayed in fig. 23, there is a difference from the 
condition just described in the presence of a few cells imbedded in 
the central mass, but clearly distinguishable from it by the nuclei 
being deeply stained. The cell-protoplasm was, however, hardly 
distinguishable from the surrounding mass. In the other example 
(fig. 21) the central mass contained no such cells. 
With the exception that it possesses no nucleus, this structure 
resembles very closely Platner’s figure of the Gasteropod ovum ', which 
contains a number of cells (‘‘ Nahrzellen’’) within its substance, 
derived from similar cells lying around the ovum. 
The first two stages described are about equal in size; the latter 
two are also about equal to each other, but considerably larger 
(twice the size) of the former. The comparison of sizes quite 
supports my identification of the latter two as the later stages in 
development ; and there can be no doubt, I think, that they all 
belong to the same series. 
These structures obviously bear a certain resemblance to the multi- 
cellular bodies in this fish and in Protopterus; and if I had not 
succeeded in finding in Ceratodus another structure undoubtedly 
corresponding to the multicellular body of Protopterus, I should have 
certainly regarded the structures at present under discussion as the 
representatives of the latter. 
The principal difference appears to be the non-formation of any 
secondary follicle-layer, the absence of any special vascular supply, 
and the fact that yolk is not formed in the early stages. With 
regard, however, to the apparent absence of the extra-follicular layer, 
it must be remembered that the close resemblance of the layer to a 
layer of stroma-cells has already been dwelt upon (p.508). It seems 
to me very possible that the structure just described is formed by 
the fusion of the protoplasm of the centrally-placed cells, the nuclei 
themselves gradually disappearing. 
An examination of better material must, however, settle the 
question. 
General Conclusions, und Comparison of Ova with those of 
other Vertebrates and Invertebrates. 
The general conclusions to be drawn from the facts, in so far as 
they refer to the Dipnoi, have been partly summed up in the résumé 
at the end of my former paper on this subject. It may be taken as 
a proved fact that the ovary in the Dipnoi contains two kinds of 
struetures developed from the germinal epithelium. The first kind 
is an ovum, the equivalent of a single cell, and is similar in all 
essentials to the cvum in the Amphibia. The second structure, 
which is very commonly met with in Protopterus and but rarely in 
1 “Zur Bildung d. Geschlechtsproducten bei den Pulmonaten,” Arch. f. mikr, 
Anat. Bd. xxvi. (1886) p. 599. 
