1907.] Wheeler, The Polymorphism of Ants. 75 



on so highly adaptive a character. Such a concise effect can hardly be due 

 to manifold and fluctuating external causes like nutrition, but must proceed 

 from some more deeply seated cause within the organism itself. Of course, 

 the difficulty here encountered is by no means peculiar to polymorphism; 

 it confronts us at every turn as the all-pervading enigma of living matter. 

 Whether we shall fare better by approaching the subject from a different 

 point of departure remains to be seen. 



4. The Phylogenetic Aspect of Polymorphism. 



An intensive study of the structure and habits of ants must inevitably 

 lead to a certain amount of speculation concerning the phylogenetic devel- 

 opment of their colonies. That these insects have had communistic habits 

 for ages is clearly indicated by the fact that all of the numerous existing 

 species are eminently social. There can be little doubt, however, that they 

 arose from forms with habits not unlike those we find today in some of the 

 solitary wasps, such as the Bembecidse, or in the remarkable South African 

 bees of the genus Allodape} Unlike other solitary wasps, the females of 

 Bemhex may be said to be incipiently social, since a number of them choose 

 a nesting site in common and, though each has her own burrow, coopei'ate 

 with one another in driving away intruders. Bembex has also taken an 

 important step in the direction of the social wasps not only in surviving the 

 hatching of her larvpe, but also in visiting them from day to day for the pur- 

 pose of providing them with fresh insect food.^ 



At a very early period the ants and social wasps must have made a fur- 

 ther advance when the mother insect succeeded in surviving till after her 

 progeny had completed their development. This seems to have led nat- 

 urally to a stage in which the young females remained with their mother 

 and reared their progeny in the parental nest, thus constituting a colony 

 of a number of similar fertile females with a common and indiscriminate 

 interest in the brood. This colony, after growing to a certain size, became 

 unstable in the same way as any aggregate of like units, and must soon have 

 shown a differentiation of its members into two classes, one of individuals 

 devoted to reproduction and another class devoted to alimentation and pro- 

 tection. In this division of labor only the latter class underwent important 

 somatic modification and specialization, while the former retained its prim- 



1 1 infer this from a brief account {in litteris) of two species of these insects, recently received, 

 together with specimens of their extraordinary larvae, from Dr. Hans Brauns of Cape Colony. 



2 Interesting accounts of the habits of this insect have been published bv Fabre (Souvenirs 

 Entomologiques. Prem. S6r., Paris, Chas. Delagrave, 1 6d., 1879; 3 M., 1894, pp. 221-234); 

 Wesenberg-Lund (Henil)ex rostrata, dens Liv og Instinkter. Eiit. Meddel. Kjiibenhavn, III, 

 1891, pp. 19-44; English r6sum6 in Psyche, VII, p. 62); and Geo. W. and Elizabeth G. Peck- 

 ham, On the Instincts and Habits of the Solitary Wasps. Wis. Geol. Nat. Hist. Surv., Bull, 

 Ho. 2, 1898, pp. 58-72. 



