58 Annals Entomological Society of America [Vol.1, 



did not follow a single upward course during the phylogeny, but 

 occun-ed repeatedly and in different phyletic groups. And since 

 the complications of polymorphism kept pace with those of social 

 organizations, we rriay say that the differentiation of the originally 

 single worker caste into dinergates, or soldiers, on the one hand, 

 and micrergates, or small workers, on the other, has been several 

 times repeated in remotely related genera. In some genera 

 (Stenamma sens, str., Leptothorax) there are also indications of a 

 lapsing of highly specialized into simpler conditions by a kind of 

 social degeneration. In its extreme form this manifests itself 

 as a suppression of castes and a consequent simplification of 

 polymorphism. Beautiful illustrations of this statement are fur- 

 nished by the parasitic species that have lost their worker caste. 

 But there are also cases in which the queen caste has been sup- 

 pressed and its functions usurped by workers (Leptogenys) . 



Not only have these greater changes been effected and fixed 

 during the phylogenetic history of the Formicidce, but also man^^ 

 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 un- 

 doubtedly 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. 

 (1894). He found by comparison with the male, which is to be 

 regarded as a relatively stable and conservative form, that the 

 cospecific females and workers may vary in stature independ- 

 ently of each other. The following are the stages which he rec- 

 ognized and some additions of my own: 



1. In the earliest phylogenetic condition, which is still pre- 

 served in the ants of the subfamily Ponerinas and in certain Myr- 

 micinae (Pseudomyrma, Myrmecina, etc.), the workers are mono- 

 morphic and of about the same size as the males and females. 



2. The worker becomes highly \-ariable in stature, from large 

 forms (dinergates, or maxima workers) resembling the female, 

 through a series of intermediates (desmergates, or mediae) to very 

 small forms (minima workers, or micrergates). This condition 

 obtains in the Dorylin^, some Myrmicinas (Pheidole, Pheidolo- 

 geton, Atta), Camponotinae (Camponotus) and Dolichoderinas 

 (Azteca) . 



