1907.] Wheeler, The Polymorphism of Ants. 51 



characteristics of the female, namely the extraordinary intricacy and ampli- 

 tude of her instincts which are thoroughly representative of the species, and 

 her ability to reproduce parthenogenetically. This, of course, means a 

 considerable degree of autonomy even in the reproductive sphere. But 

 parthenogenesis, while undoubtedly contributing to the social eflticiency of the 

 female, must be regarded and treated as an independent phenomenon, 

 without closer connection with polymorphism, for the ability to develop 

 from unfertilized eggs is an ancient characteristic of the Hymenoptera and 

 many other insects, which made its appearance among the solitary species, 

 like the Tenthredinidse and Cynipidse, long before the development of social 

 life. Moreover, polymorphism may occur in male insects which, of course, 

 are not parthenogenetic. That parthenogenesis is intimately connected with 

 sexual dimorphism, at least among the social Hymenoptera, seems to be 

 evident from the fact that the males usually if not always develop from unfer- 

 tilized, the females from fertilized eggs. 



While the bumble-bees and the wasps show us the incipient stages in the 

 development of polymorphism, the ants as a group, with the exception of a 

 few parasitic genera that have secondarily lost this character, are all com- 

 pletely polymorphic. It is conceivable that the development of different 

 castes in the female may have arisen independently in each of the three 

 groups of social Hymenoptera, although it is equally probable that they 

 may have inherited a polymorphic tendency from a common extinct ancestry. 

 On either h}^othesis, however, we must admit that the ants have carried 

 the development of female castes much further then the social bees and wasps, 

 since they have not only produced a wingless form of the worker, in addition 

 to the winged female, or queen, but in many cases also two distinct castes 

 of workers known as the worker proper and the soldier. Some systematists 

 have, therefore, appropriately separated them from all other Hymenoptera 

 as ' Heterogyna.' 



Different authors have framed very different conceptions of the phyloge- 

 netic beginnings of social life among the Hymenoptera and consequently also 

 of the phylogenetic origin and development of polymorphism. Thus Her- 

 bert Spencer evidently conceived the colony as having arisen from a con- 

 sociation of adult individuals. I infer this from his remarks on the origin 

 of the amazon colony in his well-known reply to Weismann: ^ "Some variety 

 of them [the amazon ants] led to swarm — probably at the sexual season — 

 did not disperse again as soon as other varieties. Those wliich thus kei)t 

 together derived advantages from making simultaneous attacks on prey 

 and prospered accordingly. Of descendants the varieties which carried 



' A Rejoinder to Professor Weismann. Contemp. Review, Sept. 1893, p. 14. 



