But our typical turbellarian, S. littoralis — if I 

 may be allowed even loosely to apply the word 

 typical to any specific representative of a group 

 preeminently various in its forms and marked by 

 seeming monstrosities, aberrations, and abnormal- 

 ities — although engaged in the same struggle (for 

 it is a true hermaphrodite) would appear to have 

 won not sexual independence, but freedom of an- 

 other kind. 



If we admit the fact of evolution, we must grant 

 also that it tends to operate at present from the 

 same primary impulses that caused it to operate in 

 the past. The machinery has since changed, but the 

 motive power remains the same. In other words, to 

 borrow a phrase from the philosophical biologist, 

 natural selection is governed by immutable laws. 

 Now, even were this not true, it yet remains that 

 there prevail in Nature two laws which, in what- 

 ever light we may view these matters, are as fixed 

 as they are fundamental: these laws have to do 

 solely with the mechanism of digestion and the 

 mechanism of sex, but they determine the existence 

 of the species, whether it be that of the ameba or 

 of man; and they may be exemplified in the one 

 as the simple urge to eat and the urge to repro- 



[181] 



