1890 ON WEISMANN'S THEORY 221 



SO that the arrest may have been brought about in 

 these cases by natural selection ? 



If you deem the ' chief difference ' between Dar- 

 win's and Weismann's theory of heredity to be ' that 

 the one impHes material particles and the other only 

 physical and chemical constitution,'' then, it seems to 

 me, Weismann's theory will become identical with 

 Herbert Spencer's — seeing that this is virtually the 

 only respect in which Spencer's differs from Darwin's. 

 But I think there is another and a much more 

 important respect in which W.'s theory differs from 

 both these predecessors. However, to proceed to the 

 next point, I agree with you, that the sole object of 

 the Sphex stinging the larvae is now to cause them 

 to ' keep,' and that natural selection must have 

 worked upon this for perfecting the instinct. But 

 the point is, what was the origin of the selective 

 stinging? If merely chance congenital variations, 

 would unity to billions express the chances against 

 their ever arising ? Get some mathematician to cal- 

 culate — giving as data superficial area of caterpillar 

 on the one hand and that of nine ganglia on the other. 

 Even neglecting the consideration that the variation 

 must occur many times to give unaided natural 

 selection a chance to fix it as an instinct, the chances 

 against its occurring only once would be represented 

 by the following series, where x is the superficial area 

 of the caterpillar minus that of eight gangha, and 

 tmity is superficial area of one gangha : 



xxxxxxxxx 

 If, as I suppose, x may here be taken as = 100,000, 



