FUSION OF EPIBLASTIC LAYERS IN RABBIT AND FROG. 165 



On the Phenomenon of the Fusion of the 

 Epiblastic Layers in the Rabbit and in 

 the Prog. 



By 

 Richard Asslicton, M.A. 



With Plate 18. 



In my paper upon the early stages of the development of the 

 rabbit I have given evidence in support of the views held by 

 Balfour and Heape concerning the fate of the outer layer of 

 epiblast over the embryonic disc of the rabbit embryo of the 

 seventh day. The two layers of epiblast gradually fuse together^ 

 and cells from each take part in the formation of the permanent 

 epiblast. 



In the description I have given of the process, and in the 

 attempt I have made to explain how the fusion is brought 

 aboutj I have regarded the phenomenon as being entirely 

 accidental and of no morphological importance. 



It is, however, only right to point out that there is a fusion 

 of two epiblastic layers in certain Amphibians which seems to 

 have a deeper meaning, and to which in some way the condi- 

 tion in the rabbit may be comparable. 



As far as I know, there is no account published of this 

 phenomenon, and I am not aware that anyone else has 

 noticed it. Therefore, it seems to me, a short account of the 

 facts as they appear in young embryos of Rana temporaria 

 may be of some interest. 



For the purpose of following the fusion of the two epi- 



