520 JSR. F. E. BEDDAUD ON THE DEVELOPMENT AND [DeC. 7, 



State of preservation, but iu most cases the nuclei were very vyell 

 preserved indeed, showing the rounded or oval form and the granular 

 contents. This will not apply to the germinal vesicle of the ova, 

 which were usually rather altered, showing, however, the peripheral 

 layer of germinal spots. It does not seem likely, therefore, that the 

 structure just described has been so altered as to render its identi- 

 fication impossible. 



As already said, the evidence of the existence in Ceratodus of 

 the structure formed by a fusion of cells depends upon only one 

 case, which is an early stage corresponding to that of Protopterus 

 figured on Plate LIII. fig. 9. This is the only example that 

 I have succeeded in finding after a careful examination of many 

 hundred sections. Besides these, my sections of the ovary contain a 

 few pecuHar structures, displayed in figs. 3, '21-23, which are cer- 

 tainly not referable to the same series as the last, and concerning 

 the nature and homologies of which I am in great douht. The 

 material at my disposal was not sufficiently well preserved to enable 

 me to speak with certainty as to every detail of structure ; and I only 

 succeeded in finding a very few of the bodies in question, so that the 

 following account is necessarily meagre. 



In fig. 3 of Plate LI I. is represented what I believe to be the 

 earliest stage : it consists of a spherical mass of cells bounded 

 externally by an apparently structureless membrane, which separates 

 them from the surrounding ovarian stroma (a) ; the cells are mainly 

 disposed round the periphery of the sphere, the centre of which is 

 largely occupied by spaces in which there is no trace of any fluid ; 

 the cells are small and rounded, with a large spherical or oval nucleus ; 

 the nucleus, but not the cell-protoplasm, is deeply stained by the 

 reagent used (borax carmine). The cells are exactly similar to the 

 germinal cells so far as I could see ; and the conditions I shall 

 describe in the next stage lead me to infer that they are derived 

 from the germinal epithelium. 



The second stage differs from that just described in being still 

 continuous with the germinal epithelium ; this fact would seem to 

 point to its being an earlier stage than that just described, were it not 

 for another difference in its structure. The body consists, like the 

 last stage, of a mass of cells, but in the interior is a patch of gra- 

 nular substance, which shows a different reaction to the staining- 

 fluid. It is hardly at all affected by the borax carmine and has a 

 yellowish tinge. This central mass encloses here and there a few of 

 the more peripherally-placed cells. 



Of the next two stages, displayed in figs. 21-23, I am uncertain 

 which ought to be regarded as the earlier. 



In both the mass of cells has dwindled down to a single layer of 

 peripherally-placed cells {b), which, as before, are separated from the 

 stroma of the ovary by a conspicuous and apparently structureless 

 membrane. In the centre of the cells is a spherical or oval mass of 

 a substance somewhat granular in appearance, which is not separated 

 from the peripheral layer of cells by any membrane, but only by 

 shrinkage. This mass (figs. 21 and 22) is of a yellowish tint, hardly 



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