506 MR. F. E, BEDDARD ON THE DEVELOPMENT AND [Dee. 7, 
from fishes which had been preserved entire in alcohol, and was 
unfortunately not in a very first-rate condition for microscopical 
investigation. I have been able, however, to make out the 
important fact that there is an essential similarity in the structure 
of the ovarian ova in both forms, and that in Ceratodus, as in 
Protopterus, there are, besides the ova, certain other structures 
resembling ova in many particulars which have a different mode 
of development. The discovery of this fact in Ceratodus renders it 
practically impossible to suppose that the remarkable processes in 
the development of the germinal cells of Protopterus, described and 
figured by myself in this and my last paper, are in any way abnor- 
mal; it had occurred to me before that there might be something 
abnormal. 
It cost me a great deal of labour, in the way of cutting sections, 
to ascertain that there was an actual resemblance between Ceratodus 
and Protopterus. In my specimen of Protopterus I found it quite 
impossible to make a section of the ovary anywhere without dis- 
covering ova of both kinds in nearly equal abundance ; in Ceratodus, 
on the other hand (and this statement applies to two specimens), ova 
of the second kind were extremely rare; I have cut literally hundreds 
of sections without coming across any evidence of the existence of two 
kinds of ova. This may be a real difference between the two genera, 
or may depend upon the season of the year at which the specimens 
were captured. In every case, however, the ovaries contained 
numerous mature ova, though the number of these latter was very 
much less than that of the immature ova. 
On the other hand, it is possible that there is really a difference in 
this respect between Protopterus and Ceratodus, which show other 
important anatomical differences. 
I have already contributed to the ‘Zoologischer Anzeiger’ (No. 236) 
a brief note of the principal facts contained in this paper. 
I have but little to add to my former paper on the structure of 
the ordinary ova of Protopterus. 
In my last paper I drew attention to the curious specialization of 
the yolk in the adult ova; in fig. 4 of plate xxviii. of that paper is 
illustrated an adult ovum which shows a differentiation of the yolk 
into two distinct layers, which are less distinguishable by their 
coloration or arrangement of yolk-particles than by the very definite 
break which separates them. ‘he outer layer of yolk forms a com- 
paratively thin envelope, the greater portion of the ovum being 
occupied by the central mass of yolk. 
Van Bambeke’ has recently noted and figured a similar condition 
of the ripe ovum in Godius niger and other fishes, and Pfliiger had 
previously referred to the same phenomenon in Mammalia. Ac- 
cording to Van Bambeke, the distinction between the two zones 
occasionally disappears under the influence of reagents. Van Bam- 
beke speaks of the line of division which separates the two zones as 
not being a membrane, but merely a condensation of the egg- 
protoplasm. With this opinion I fully agree: in the first place, the 
1 Arch. d. Biol. t. iv. (1885). 
