506 MR. F. E. BEDDARD ON THK DEVELOPMENT AND [DeC. 7, 



from fishes which had been preserved entire in alcohol, and was 

 unfortunately not in a very first-rate condition for microsco|)ical 

 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 Geratodus, as in 

 Protopterus, there are, besides the ova, certain other structures 

 resembling ova in many particulars which have a different mode 

 of development. Tlie 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 pa])er, 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. The 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 Gobius 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 iully agree : in the first place, the 

 1 Arch. d. Biol. t. iv. (1885). 



