THE FUNGUS-GROWING ANTS. 



319 



with their substratum, or nutriment by the ants, and in turn supply 

 these insects with their only food. 



The Attii, of which about one hundred species, subspecies and 

 varieties have been described, are all fungus-growers and -eaters. The 

 tribe ranges from about 40 S. to 40 N. of the equator, but is best rep- 

 resented in the tropics. The species have been assigned to five genera, 

 which, beginning with the most primitive, are Myrmicocrypta, Cypho- 

 myrmex, Apterostigina, Sericomyrmex and Atta. The last of these is 

 divided into six subgenera : Mycocepurus, Mycetosoritis, Trachymyr- 

 mex, Mcellerius, Acromynue.v and Atta s. str. The subgenus Atta 



FIG. 185. Worker of 

 Apterostigma pilositm of 

 Brazil. (Original.) 



FIG. 1 86. Two species of Cyphomyr- 

 mex occurring in the United States. (Orig- 

 inal.) a, C. riniosiis; b, C. ivheeleri. 



comprises the leaf-cutting, or parasol ants, the largest and most pow- 

 erful species of the tribe, living in great colonies and inhabiting the 

 territory between 30 north and 30 south of the equator. The workers 

 are highly polymorphic and much smaller than the males and females. 

 The colonies of the species of MarHerins and Acromyrmex are much 

 less populous, and the workers, though variable in size, do not exhibit 

 such marked polymorphism as those of Atta s. str. In Trachymyrme.r 

 and the remaining subgenera the workers are monomorphic and but 

 little smaller than the males and females, and the colonies are even 

 feebler than those of Acromyrmex. Mycetosoritis and Mycocepurus 



