52 THE EVOLUTION OF SEX. 



And why not ? This denial of the inheritance of dints from 

 without, and of acquired habits other than constitutional, can 

 be no mere optimism on Weismann's part. It is, he maintains, 

 a scientific scepticism, based on the one hand on the absence 

 of data demonstrating what we may still call the current belief, 

 and on the other hand on the improbability of changes pro- 

 duced as above explained reacting from the " body " on the 

 reproductive cells. If such a reaction do not occur, Weismann's 

 position is secure ; and though in a system saturated with 

 alcohol, or transferred to a new climate, the reproductive cells 

 may vary alotig with the body, no modification of nerve or 

 muscle can, as such, be transmitted in inheritance. In short, 

 the reproductive protoplasm must be in a sense insulated, and 

 leads a charmed life away from external disturbance. 



This view, supported as it is by many authorites, is obviously 

 of the utmost importance, both for the general theory of evolu- 

 tion, and for such practical problems as those of the pathologist 

 and the teacher. Its full consideration is here impossible, 

 involving matter enough for a special treatise on heredity. 

 The difficulty of any yea or nay lies in the relative scarcity of 

 experimental data, in the divergence of opinion as to the 

 pathological evidence, and very largely in the difficulty of 

 applying our logical or anatomical distinctions to the intricate 

 facts of nature. Thus the distinction between "acquired," and 

 germinal or constitutional, is easily made on paper, but is 

 difficult in actual practice ; nor is the line between a variation 

 of the reproductive cells, along with the body, and one produced 

 by the body, readily drawn in concrete cases. 



One criticism is suggested by the present chapter. The 

 assumed insulation or separateness of the reproductive elements 

 from the general life of the body, how far is this real ? In view of 

 the genuine unity of the organism, a charmed Hfe of one of the 

 systems seems to some a "veritable physiological miracle;" and 

 therefore we point to such a case as Yung's tadpoles, where an 

 outside influence of nutrition saturated through the organism 

 and did affect the reproductive elements, not indeed to the 

 degree of altering any structural feature of the species, but yet 

 to the extent of altering the natural numerical proportions of 

 the sexes. 



