4 6 THE EVOLUTION OE SEX. 



not occur, Weismann's position is secure; and though in a system 

 saturated with alcohol, or transferred to a new climate, the repro- 

 ductive cells may vary along 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 authorities, is obviously of 

 the utmost importance, both for the general theory of evolution, 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 

 applving 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 life 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 repro- 

 ductive 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. 



