1907.] Wheeler, The Polymorphism of Ants. 77 



lias been repeated in remotely related genera. In .some genera (Stenamma 

 sens, str., Leptothorax) there are also indications of a lapsing of highly special- 

 ized into simpler conditions by a kind of social degeneration. In its extreme 

 form this manifests itself as a suppression of castes and a consequent sim- 

 plification of polymorphism. Beautiful illustrations of this statement are 

 furnished by the parasitic species that have lost their worker caste. But 

 there are also cases in which the queen caste has been suppressed and its 

 functions usurped by workers. 



Not only have these greater changes been effected and fixed during the 

 phylogenetic history of the Formicidfe, but also many subtler differences 

 such as those of stature, coloration, pilosity and sculpture. And although 

 such differences belong to the class of fluctuating variations and are usually 

 supposed to have a greater ontogenetic than phylogenetic significance, they 

 are undoubtedly of great antiquity and must therefore be regarded as more 

 important than many of the minor morphological traits. 



Emery was the first to call attention to a number of peculiar phylogenetic 

 stages in the development of stature among ants.^ We find by comparison 

 with the male, which may be regarded as a relatively stable and conservative 

 form, that the cospecific females and workers may vary in stature inde- 

 pendently of each other. The following are the stages recognized by 

 Emery, with some additions of my own: 



1. In the earliest phylogenetic condition which is still preserved in the 

 ants of the subfamily Ponerinse and in certain Myrmicinae {P.seudomyrma, 

 Myrmecina, etc.), the workers are monomorphic and of about the same size 

 as the males and females. 



2. The worker becomes highly variable in stature from large forms 

 (dinergates, or maxima workers) resembling the female, through a series of 

 intermediates (desmergates) to very small forms (minima workers, or micrer- 

 gates). This condition obtains in the Dorylinee, some iNIyrmicinpe, (some 

 species of Pheidole, Pheidologeton, Atta), Camponotinje (Camponotus) and 

 Dolichoderinse (Azteca). 



3. The worker becomes dimorphic thi'ough the disappearance of the 

 desmergates, so that the originally single, variable caste is now represented 

 by two, the soldier (dinergate) and worker proper. We find this condition 

 in certain ]Myrmicinje and Camponotinje (Cri/ptocerns, Pheidole, Aeantho- 

 myrmex, Colohopsis, etc.). 



4. The soldier of the preceding stage disappears completely, so that the 

 worker caste again becomes monomorphic but is represented by individuals 

 very much smaller than the female. Such individuals are really micrergates. 



' Die Entstehung und Ausbildung der Arbeiter bei den Ameisen, loc. cit., pp. 55, 56. 



