EARLY STAGES OF DEVELOPMENT OF THE RABBIT. 149 



scattered hypoblast cells have now become much more numer- 

 ous, and are scattered more evenly over the portion of the wall 

 upon which they are to be found. Many of them, possibly 

 all of them, are now undoubtedly connected by more or less 

 fine protoplasmic threads. 



These scattered cells, although such conspicuous objects 

 during the fifth day, are now extremely difl&cult to make out, 

 and can very easily escape notice. 



They are more numerous now nearer to the embryonic disc, 

 and merge gradually into the continuous layer just described. 

 They are now very much more flattened. 



Towards the line of their outer limit they present more the 

 characters of the former day, being fewer and rather rounded 

 and more isolated. 



Consideration of the Extent to which the Shape 

 of the Cells of the several Layers may be attri- 

 buted to Mechanical Causes. 



At this time we find cells of two very different types, with 

 cells showing all intermediate stages between the two. 



The first type is the rounded, almost completely isolated cell, 

 such as those of the inner layer of epiblast, or near the outer 

 limit of the hypoblast ; the second type is the flattened or 

 stretched cell of the outer layer of epiblast or embryonic hypo- 

 blast, continuous with its neighbours around all its edges; and 

 thirdly, forms of cells intermediate between these two types. 

 How far can we hold this diff'erence of form to be due to the 

 environment of the individual cell apart from its own inherited 

 tendencies ? 



Whether there is any cell in the embryo at this time quite 

 separated from all others I am not certain. Of course they are 

 all contiguous to one or more other cells, but possibly there is 

 an actual protoplasmic union between one cell and another. 

 This is certainly the case very frequently with the cells of 

 the hypoblast, which at first sight seem to be quite separate. 



In sections, and in surface views, there is no distinct connec- 

 tion to be made out between the rounded cells of the inner 



