i88 Darwin and Romanes dealt with. 



flexible) becomes exactly like that of the female. No 

 man will surely deny that here is a case where an 

 accommodating instinct, passive if not active, in the 

 preyed upon becomes absolutely of benefit to the 

 parasitic species, and of loss and injury only both to 

 the individual and to the species protecting. Here 

 are structures which become essentially modified in 

 favour of an alien parasitic species — just as the 

 parental instinct in victims of cuckoo become modi- 

 fied — and one effect of that change of structure is 

 sterility in both male and female, where instinct of 

 protection has been assenting and is a cause. The 

 delicacy and susceptibility of the generative organs 

 to which Darwin at last awakened are testified by 

 such vast changes as this as well as by those he 

 noticed and dwelt on. 



In other cases, as well in plants as in animals, 

 there are nothing short of voluntary (we can use no 

 other word) self-adaptations to the entertainment of 

 the parasite. 



There are certain blind beetles ( Staphylinidce ) found 

 in anthills living at the expense of the ant commun- 

 ity, and, so far as can be ascertained, yield no service 

 or benefit whatever to the ants in return. The in- 

 stinct of the ants, which tolerates and leads them 

 even to protect the beetles, is surely an instinct en- 

 tirely in favour of the beetles, and of no service to 

 the ants. 



" Although the fact is not yet proved," says Van 

 Beneden, " it is at any rate very likely that at an 

 earlier period there had subsisted between these 

 species and the ants some kind of mutualist relation 

 analogous to that which still exists between ants and 



