556 Saw-flies, Gall-flies, Ichneumons, 



ment by which the differences are produced. The fact that the social insects 

 in which the phenomena of caste or polymorphism occur, though belonging 

 to very diverse groups, all feed their young, is of itself very suggestive. When 

 we add to this the fact that in ants, where the phenomena of polymorphism 

 reach their highest complexity, the food is elaborated in their own organs 

 by the feeders that administer it, it appears probable that the means of pro- 

 ducing the diversity may be found herein." 



The answer to the second query a query anticipated by the keen-minded 

 Darwin as voicing an apparently insuperable objection to the selection 

 theory as made in the Origin of Species at the end of the chapter on Instinct 

 has, by the investigation of modern students of ants, only been strengthened. 

 This answer made by Darwin, and repeated with new supporting observa- 

 tions and ingenious arguments by the present-day Neo-Darwinians, is briefly: 

 that the differences between the queens and the various worker castes are 

 quantitative rather than qualitative, that gradatory conditions exist between 

 the extreme points of the various lines of structural and physiological speciali- 

 zation, individuals being found in almost every ant species, so far carefully 

 studied, standing as connecting links between queen and highly specialized 

 infertile worker (or soldier); that there has been a gradual achievement 

 of this differentiation of structure through the advantage to the species of 

 the slight congenital tendencies toward sterility on the part of some of the 

 young, and by consequence their special devotion to the nest industries, leav- 

 ing the fertile individuals freer for reproductive activity; that the evolution 

 has been one of communities rather than of individuals; that those fertile 

 males and females have persisted which have shown a tendency to produce 

 some sterile individuals among their progeny which, living in consociation 

 with the fertile individuals of the brood, were of special advantage to the 

 community more and more as they possessed such variations of structure 

 as would fit some for general work and others for the special defence of the 

 colony; and, finally, that such advantages to the community have been 

 quite sufficient as handles for the action of natural selection, with the final 

 result as seen to-day in developing ant species in which there is a fairly sharp 

 division between fertile and sterile forms, and between two or three different 

 castes of the sterile individuals. Those species are the modern ones whose 

 fertile females produce several well-modified kinds of individuals. Darwin 

 and the Neo-Darwinians of to-day not only find in this answer an adequate 

 explanation of the development of the modern highly specialized ant com- 

 munity by the action of natural selection, but find the existence of such com- 

 munities a convincing fact telling against the belief of Lamarckians and 

 Neo-Lamarckians in evolution by the accumulation of inherited structural 

 and physiological characters acquired in the lifetime of individuals. As 



