294 Darwin, and after Darwin. 



the first instance, or if the needs of the insect progeny 

 had not been such as to have derived profit from 

 being enclosed in such a tumour, then, of course, the 

 inoculating instinct of these animals could not have 

 been developed by natural selection. But given these 

 two conditions, and it appears to me there is nothing 

 very much more remarkable about an accidental 

 correlation between the effects of a parasitic larva on 

 a plant and the needs of that parasite, than there is 

 between the similarly accidental correlation between 

 a hydated parasite and the nutrition furnished to it by 

 the tissues of a warm-blooded animal. Doubtless the 

 case of galls is somewhat more remarkable, inasmuch 

 as the morbid growth of the plant has more concern 

 in the correlation — being, in many instances, a more 

 specialized structure on the part of a host than occurs 

 anywhere else, either in the animal or vegetable world. 

 But here I may suggest that although natural selection 

 cannot have acted upon the plant directly, so as to have 

 produced galls ever better and better adapted to the 

 needs of the insect, it may have so acted upon the 

 plants indirectly through the insects. For it may very 

 well have been that natural selection would ever 

 tend to preserve those individual insects, the quality 

 of whose emanations tended to produce the form of galls 

 best suited to nourish the insect progeny ; and- thus 

 the character of these pathological growths may have 

 become ever better and better adapted to the needs 

 of the insects. Lastly, looking to the enormous 

 number of relations and inter-relations between all 

 organic species, it is scarcely to be wondered at that 

 even so extraordinary an instance of correlation as 

 this should have arisen thus by accident, and then 



