158 EICHARD ASSHETON. 



{EP. I.). The outline of cells is hardly visible. Here and 

 there, as though filling up interstices, are cells which stain 

 much more darkly (EP. 0.), and in the character of their 

 nuclei appear more like the cells of the outer epiblast beyond 

 the border of the embryonic disc. Some of these are only 

 little wedge-shaped bodies on the surface (fig. 32, EP. 0.), 

 others pass right through ; others seem to send flaps over the 

 surface of the inner layer cells (fig. 33, EP. OR.). The last- 

 named cell (fig. 33, EP. OR.) is very curious. It will be 

 noticed there are several rather like it. These almost look as 

 though they were being enclosed quite accidentally by the 

 inner layer of cells. It seems to me quite possible for this to 

 be very often the case. Take such a spot as that to which the 

 line EP. 0. runs in fig. 30; here, of course, the bend in the 

 outer layer is in all probability artificial. But if a gap existed, 

 as frequently happens, between the cells of the inner epiblast, 

 then if at a neighbouring spot the outer layer became ruptured, 

 the tension would be removed, and the Kauber cell might very 

 well become enfolded quite passively, as I believe is taking 

 place in fig. 33, EP. 0. R. There is no reason why a cell 

 thus enfolded should die, in all probability it would grow and 

 multiply like any other cell of the region. 



(It may be observed that of all the cells in the whole blasto- 

 dermic vesicle at this time, none are so badly placed for nutri- 

 ment [provided we allow that nutriment is all the time being 

 received from the fluids of the uterus] as the cells of the outer 

 epiblast layer over the embryonic disc. For they here lie be- 

 tween the thickest part of the albumen layer and the thick 

 inner epiblast layer, which may account for the period of in- 

 activity of this layer at this moment.) 



I cannot leave this question without a short discussion of 

 the morphological bearings of the events connected with the 

 fusion of these two layers. 



First of all, I wish to call attention to Heape's description 

 of the mole's development. The mole is very like the rabbit 

 in its developmental history. 



Just after the separation of the hypoblast layer, Heape 



