114 RICHARD ASSHETON. 



which would of itself produce not a specific embryo, but an 

 amorphous monster unless directed by the influence of (in the 

 rabbit) inanimate coats and the walls of the uterus. 



I have come to the following conclusions upon certain dis- 

 puted points. 



(i) Van Beneden's description of the segmentation I consider 

 to be inaccurate. 



(ii) I find no trace of van Beneden's blastopore. 



(iii) I find no trace of a '^gastrulation.'^ 



(iv) There is no evidence in support of Robinson's^ specula- 

 tions concerning the existence of a hypoblastic wall to the 

 blastocyst surrounded subsequently by the epiblast. 



(v) Rauber's layer fuses with the inner layer of epil)last as 

 described by Balfour^ and Heape.^ 



(vi) This fusion has but slight morphological significance, 

 since its existence and disappearance are caused mechanically 

 by ontogenetic conditions. 



(vii) The growth round of the hypoblast is apparent only, 

 being due to the presence of a zone of specially active epiblast 

 surrounding the embryonic disc, which zone is to be considered 

 to be the equivalent of the trager in other rodents. 



I have endeavoured to show how important is the albuminous 

 layer, and how I believe that it is possible to account for 

 many details of change up to the end of the sixth day by 

 strictly epigenetic processes; and since these processes during 

 this time are almost all directed by environment as between 

 the embryo and the maternal influences rather than between 

 cell and cell of the embryo itself, it follows that the palin- 

 genetic features of the development must be reduced to a 

 minimum. 



This paper is based upon the examination of upwards of 300 

 embryos between the 24th and 168th hours. The embryos have 

 been examined fresh, and after treatment with various reagents 

 — Perenyi,osmicacid, picric acid, Flemmiug, Hermann, chromic 



• 'Quart. Journ. Micr. Sci./ vol. xxxiii. 



' ' Comparative Embryology/ vol. ii. 



' ' Quart. Journ. Micr. Sci./ vols, xxiii and xxvi. 



