126 RICHARD ASSHETON. 



centre of a rabbit embryo aged seventy-six hours and a half. 

 This was preserved in Perenyi's fluid, stained with borax 

 carmine, cut and mounted in series. The one I have drawn is 

 the fourth of eight which pass through the actual embryo itself. 



The embryo at this stage is composed of a number of cells 

 or segments, as far as I can see all similar in character, though 

 varying a good deal in size. 



The cells in the centre are no doubt pressed closely 

 together in the living state, the several clefts, with the possible 

 exception of one, being artificial. This just-mentioned excep- 

 tion, the more regular and continuous slit marked C. BL., is in 

 all probability the first commencement of the slit which ulti- 

 mately enlarges into the cavity of the blastodermic vesicle. 



In only one specimen have I found certain cells to take the 

 stain better than others. I have drawn two figures (18 and 19) 

 from the series of sections in which this occurs, in order to 

 show how such an appearance as that described and figured by 

 van Beneden (pi. iv of his paper) may arise, and at the same 

 time to show how the interpretation put on it by him cannot 

 be held to be sound. 



In this specimen the embryo has contracted very much, and 

 is lying quite free from the zona pellucida and albuminous 

 layer. 



In fig. 18 the majority of the cells at the surface are seen to 

 be slightly darker than the mass inside, with the exception of 

 two at the point x. This is undoubtedly like van Beneden's 

 figure of an optical section (pi. iv, fig. 1). But if we look at 

 another section, fig. 19, we find here that again the cells of the 

 surface layer have mostly stained darker, with the exception of 

 one at a?'. 



Hence we are obliged to believe that in this specimen there 

 existed at least two of van Beneden's blastopores, for the 

 light-coloured cells which show at the surface in fig. 18 are at 

 almost the opposite pole to that at which the lighter-coloured 

 cells of fig. 19 show at the surface. 



In sections of other specimens of about this age (seventy- 

 two hours) fixed with osmic acid 2 per cent,, I have failed also 



