1907.] Wheeler, The Pohjmorphism of Ants. 79 



The stature differences described in the above paragraphs are in most 

 if not all cases, highly adaptive. This is clearly seen in such forms as the 

 Indo-African Carebara, the huge, deeply colored females of which are more 

 than a thousand times as large as the diminutive, yellow workers. This ant 

 dwells in termite nests where it occupies chambers connected by means of 

 tenuous galleries with the spacious apartments of its hosts. The termites 

 constitute a supply of food so accessible and abundant that the workers are 

 able to rear enormous males and females, while they themselves must pre- 

 serve their diminutive stature in adaptation to their clandestine and thiev- 

 ish habits. Similar conditions are fovmd in many species of the allied genus 

 Solenopsis, which inhabit delicate galleries communicating with the nests 

 of other ants on the larvae and pupse of which they feed. In one species of 

 this genus (S. geminata) however, which leads an independent life and feeds 

 on miscellaneous insects and seeds, the worker caste is still highly poly- 

 morphic. 



Another interesting case of adaptation in stature is seen in the ants of the 

 Formica microgyna group. The females of these species are temporarily 

 parasitic in the nests of other Formicoe and are therefore relieved of the 

 labor of digging nests for themselves and rearing their first brood of larvae. 

 On this account they need not store up large quantities of food, so that the 

 nourishment which in nonparasitic species goes to produce a comparatively 

 few large females may be applied to the production of a large number of 

 small females. This latter condition is necessary in parasitic species which 

 are decimated by many vicissitudes before they can establish themselves 

 successfully among alien hosts. I have already emphasized the adaptive 

 significance of the disappearance of the worker caste among permanently 

 parasitic species like Anergates, Wheeleria, etc. 



There are several cases in which the worker and female differ greatly 

 in color, pilosity, or sculpture, and in such cases either caste may be con- 

 servative or aberrant according to ethological requirements. Thus in cer- 

 tain temporary parasites like Formica ciliata, oreas, montigena, dakotensis, 

 and difpcilis, the female is aberrant in one or more of the characters men- 

 tioned, while the cospecific worker retains the ancestral characters of the 

 same caste in the closely allied forms of F. rufa. The same condition is seen 

 in a very different ant, Aphmiogaster tennesseensls, as the result of similar 

 parasitic habits. In all of these species ihe females alone have developed 

 myrmecophilous characters, like the long yellow hairs of F. ciliata, or the 

 mimetic coloring of F. dijficilifi, which enable them to foist themselves on 

 allied species and thus avoid the exhausting labor of excavating nests and 

 rearing workers. 



The foregoing observations indicate that in their morphological charac- 



