60 THE ORGANIC GROWTH OF THE LIVING WORLD sec. 



That the male outstrips the female in phyletic growth is 

 comprehensible apart from the importance of adaptation in 

 this process, from the greater strength developed in the 

 former ; and that the growth of new characters shows itself 

 first in the later period of life, in the period of most complete 

 development, at the end of the ordinary and general develop- 

 ment, is comprehensible, again apart from the importance of 

 adaptation, merely from my theory of growth. 



This view of mine is, however, further supported by the 

 fact that an essential cause of male preponderance consists in 

 the appearance of characters during the breeding period, at 

 the time of maximum vigour, many of which are subsequently 

 transmitted by heredity first as constant male characters, and 

 finally to the whole race. These characters include not merely 

 colour and strongly developed markings, — a long series of 

 male characters could be mentioned which were evidently 

 only present originally as such sexual distinctions in the 

 male. And we know many instances in which such characters 

 are intensified to a surprising degree in the males at the 

 breeding period, as, for instance, the dorsal crest of many 

 w^ater newts (Tritonidae), the hook-shaped prolongation of the 

 lower jaw in salmon and trout. In this sense it is an interest- 

 ing fact that the latter formation becomes permanent in old 

 male salmon, so that such hook-jawed specimens have been 

 considered as forming an independent species. 



The facts referred to in the preceding : (1) the definite 

 directions of evolution ; (2) the appearance of new characters 

 at definite regions of the body, and their progress in an un- 

 varying direction during individual life ; (3) the symmetrical 

 or in some cases metameric occurrence of characters ; (4) the 

 first occurrence of characters at a late period of life, as it were 

 at the end of the stage of evolution previously attained ; (5) 

 their first occurrence at the time of the maximum develop- 

 ment of vigour — these facts I might point to as not merely 



