74 Bulletin American Museum, of Natural History. [Vol. XXIIl, 



In commenting on this hypothesis of a struggle of the parts in connection 

 with the mermithergates, I have already shown (p. 26) that it is inapplicable 

 to the cases which first suggested it. This does not, however, disqualify it 

 as a possible explanation of the normal worker forms. It does, indeed, 

 appear to give us an insight into the possible conditions of development in 

 the starved larvae from which the workers arise and suggests interesting 

 problems for the experimentalist. Still it is incomplete and like the other 

 views considered in the preceding paragraphs, fails to account for the highly 

 adaptive structure of the worker. 



There lurks, perhaps, in Emery's hypothesis a suggestion of a wide- 

 spread notion that there is something monstrous, teratological or hypertelic, 

 about the w^orkers and especially about the soldiers of the social insects. 

 This is more explicitly stated in the above-quoted passages from Spencer 

 and Marchal (pp. 60, 65). The latter, in fact, regards the rearing of the 

 sterile forms as a kind of experimental teratogeny. Such an impression 

 is very natural, for the soldiers of many ants and termites certainly exhibit 

 developments of the head and mandibles unlike anything found in other 

 insects. And it is not impossible that these castes may have orginally 

 made their appearance as teratological developments. But that they are 

 such at the present time is very improbable, since we find that they are not 

 only normal and all-important constituents of the colony, but have become 

 exquisitely adapted to particular functions. Wherever the habits of the 

 soldiers have been carefully studied it has been found that their singular 

 and apparently hypertrophied structures have a very definite function. 

 Thus it has been shown that the peculiarly truncated heads of the Colobopsis 

 soldiers are used as "animated front-doors" in closing the circular entrances 

 to the galleries of the nest, that the colossal crania of the Pheidole soldiers 

 accommodate the huge muscle-masses of the jaws which in turn are used in 

 cracking hard seeds and the tough integument of insects, and that the pecul- 

 iar sickle-shaped mandibles of the soldiers of Myrmecocystus hombycinus are 

 used for carrying the voluminous pupfe.^ It is very probable that in ter- 

 mites the singular heads of the nasute and mandibulate soldiers will be found 

 to be similarly adapted to special functions in the economy of the colony. 

 At any rate we are not justified in regarding such structures as hypertelic 

 or teratological till we know more about the habits of the species in which 

 they occur. 



We may conclude, therefore, that while the conception of the worker 

 type as the result of imperfect nutrition is supported by a considerable vol- 

 ume of evidence, we are still unable to understand how this result can take 



1 See Escherich, Die Ameise, loc. cit., p. 46. 



