30 PARA. Chap. T. 



intercross with members of distant colonies whicli swarm 

 at the same time, and thereby increase the vigour of 

 the race, a proceeding essential to the prosperity of any 

 species. In many ants, especially those of tropical 

 climates, the workers, again, are of two classes, whose 

 structm'e and functions are widely different. In some 

 species they are wonderfully unlike each other, and 

 constitute two well-defined forms of workers. In others, 

 there is a gradation of individuals between the two 

 extremes. The curious differences in structure and 

 habits between these two classes form an interesting, 

 but very difficult, study. It is one of the great pecu- 

 liarities of the Saiiba ant to possess three classes of 

 workers. My investigations regarding them were far 

 from complete ; I will relate, however, what I have 

 observed on the subject. 



When engaged in leaf-cutting, plundering farinha, 

 and other operations, two classes of workers are always 

 seen (Figs. 1 and 2, page 24). They are not, it is true, 

 very sharply defined in structure, for individuals of in- 

 termediate grades occur. All the work, however, is 

 done by the individuals which have small heads (Fig. 1), 

 whilst those which have enormously large heads, the 

 worker-majors (Fig. 2), are observed to be simply 

 walking about. I could never satisfy myself as to the 

 function of these worker-majors. They are not the 

 soldiers or defenders of the working portion of the com- 

 munity, like the armed class in the Termites, or white 

 ants ; for they never fight. The species has no sting, 

 and does not display active resistance when interfered 

 with. I once imagined they exercised a sort of super- 



