414 NATURAL SCIENCE. June. 1897. 



" (i) The direction of the first plane of segmentation and the 

 planes of the embryo's body are independent of, and have no 

 causal relation to, each other. 



•' (2) The process of segmentation does not result in the division 

 of nuclear material into qualitatively dissimilar portions 

 which determine the development of different parts of the 

 body. 



" (3) The fact that, in many cases, the planes of segmentation 

 coincide more or less with the axes of the embryonic body, 

 and that individual primitive organs are developed from 

 definite areas on the surface of the ovum, is simply a con- 

 sequence of the structure of the ovum itself, of its form, and 

 of the distribution of protoplasm and reserve-material." 



The book is written throughout in the author's usual lucid and 

 readable style ; the appendix is illustrated by a few diagrammatic 

 figures which render the somewhat involved statements of Roux more 

 intelligible ; and there is an ample bibliographical list of works to 

 which reference is made, as well as some additional notes. 



L. J. Veley. 

 22 Norham Road, Oxford. 



