﻿CURRENT LITERA TI Kl, 



cence, its greater instability." 



"Moreover, the course of development of the gametes bears every indication of 

 being a progressive differentiation and senescence, not fundamentally different from 

 that of other organs of the body, and the fully developed gametes are physiologically 

 old, highly differentiated cells which are rapidly approaching death and in most cases 

 actually do die soon after maturity, unless fertilization occurs. These cells must be 



undergoing dedifferentiation and reconstitution i 



Physiologists should be particularly interested in this theory. For the 

 first time we have an explanation of the processes of morphogenesis which is 

 essentially physiological, and which may be tested by physiological methods. 

 The control of the growing tip, or the rapidly metabolizing head end of the 

 animal, is supposed to be exerted on the parts less active by means of something 

 of the nature of nerve impulses spreading from one region to the other. This 

 conception will undoubtedly appeal to the majority of physiologists. Simi- 

 larly, for the first time we have at least the foundation of a physiological 

 explanation of the manner in which, from a simple germ, a highly differentiated 

 adult will and must arise. The morphological conception of pangenes is 

 entirely abandoned. The book is thus essentially constructive, and not a 

 destructive criticism only of such views. To the pharmacologist the dis- 

 covery of the cause of the sensitivity of the nervous system to drugs of all kinds 

 and its relation to metabolism is a matter of very great interest and importance. 

 To the ordinary man of a philosophical temperament this book must appeal 

 for its solid thoughtfulness, clear exposition, and cautious conclusions. The 

 large number of well executed illustrations greatly adds to the ease of following 

 the text. Zoologist's and botanists have here a theory which offers an explana- 

 tion of the most interesting and obscure of their phenomena. It presents a 

 possible and apparently a practicable means of escape from neo-vitalism.— 

 A. P. .Mathews. 



