1907.] Wheeler, The Polymorphism of Ants. 85 



including, of course, those of alimentation and nest-building, become merely 

 tributary or ancillary. In ants, especially, the instincts relating to the nur- 

 ture of the young bear the aspect of a dominating obsession. The very 

 strength and scope of such instincts, however, renders these insects more 

 susceptible to the inroads of a host of guests, commensals and parasites, 

 besides the parasitic larvpe of Chalcidids, Lomechusini and Metopina de- 

 scribed in the first part of this article, there are many adult beetles and other 

 insects on which the ants lavish as much or even more attention than they do 

 on their own brood. And when the ants themselves become parasitic on 

 other ants, it is always either for the sake of having their own brood nur- 

 tured, as in the temporarily and permanently parasitic forms, or for the 

 purpose of securing the brood of another species, as in the slave-making, 

 or dulotic species. 



The philoprogenitive instincts arose and were highly developed among 

 the solitary ancestral insects long before social life made its appearance. 

 In fact, social life is itself merely an extension of these instincts to the adult 

 offspring, and there can be no doubt that once developed it reacted rapidly 

 and powerfully in perfecting these same instincts. It is not so much the 

 fact that all the activities of the social insects converge towards and center in 

 the reproduction of the species, for this is the case with all organisms, as the 

 elaborate living environment developed for the nurture of the young, that 

 gives these insects their unique position among the lower animals. A full 

 analysis of the threptic activities would involve a study of the entire ethol- 

 ogy of the social insects and cannot be undertaken at the present time. 

 Nevertheless the bearing of these instincts on the subject of polymorphism 

 can hardly be overestimated and deserves to be emphasized in this connection. 



All writers agree in ascribing polymorphism to a physiological division of 

 labor among orginally similar organisms. This is tantamount to the as- 

 sumption that the phylogenetic differentiation of the castes arose in the 

 sphere of function before it manifested itself in structural peculiarities. 

 Although this view implies that the female, or queen, Avas the source from 

 Avhich both the instincts and structures of the worker were derived, it has 

 been obscured by an improper emphasis on the instincts of the honey-bee, 

 in which the female is clearly a degenerate organism, and on certain special- 

 ized instincts, supposed to belong exclusively to worker ants like the slave- 

 makers (Polyergus and Formica sanf/uinea) . We have therefore to consider, 

 first, the instincts of the queen and, second, any evidence that may go to 

 show that instinct-changes precede morphological differentiation in the 

 phylogcny of the species. 



It is evident that the social insects may be divided into two groups 

 according to the instinct role of the (jueens. In one group, embracing the 



