46 Bulletin American Museum of Natural History. [Vol. XXII, 



begin to usurp the functions of the mother ant. They manure the 

 garden, which at the time of their appearance measures hardly 

 more than 2.5 cm. in diameter, and feed the larvae with their mother's 

 eggs. The workers themselves, however, feed on the "kohlrabi" 

 which has been developing on the hyphae for some time. After 

 about a week some of the workers begin to dig in the earth, and 

 ten days after the appearance of the first worker and seven weeks after 

 the inception of the colony, they break through to the surface of the 

 soil and surround the entrance of the nest with a tiny crater of earthen 

 pellets. They now begin to bring in pieces of leaves, knead them up 

 into minute wads, and insert them in the fungus garden. The method 

 of manuring the garden with fecal droplets seems now to be abandoned. 

 The mother Atta henceforth pays no attention to the development of 

 the garden or to the brood, but degenerates into a sluggish, egg-laying 

 machine, while the multifarious labors of the colony devolve on the 

 workers. In the meantime the "kohlrabi" has become so abundant 

 that it can be fed to the larvae. 



In concluding his paper Huber makes the important observation 

 that fertile females of Atta sexdens are readily adopted by strange 

 workers of their own species. Such adoptions may be frequently re- 

 sorted to in a state of nature and would perhaps account for the 

 enormous size and great age of some of the formicaries of the larger 

 species of Atta, which in this respect resemble the colonies of Formica 

 rufa and F. exsectoides in the north temperate zone. 



In marked contrast with the elaborate habits and great indepen- 

 dence of the Atta females are those of certain ants which are unable 

 to establish their colonies without the assistance of alien workers. 

 Some of the most remarkable examples of this inability are found in 

 the typical genus Formica. 



Our American species of Formica may be separated into at least five 

 groups, all but one of which may bear the name of a well-known Eu- 

 ropean species. America is, without doubt, the geographical center of 

 the genus and hence an American type for each group would seem to be 

 more appropriate. Nevertheless, both because the European species 

 were first and more thoroughly studied and because they are less 

 variable than their American congeners, they should maintain their 

 position as reference types. The five groups of species are the follow- 

 ing: 



I. The fttsca group. European type: F. fusca Linn. Typical and 

 most widely distributed American form: F. fusca var. subsericea Say. 

 Additional varieties: subcenescens Emery, argentata Wheeler, gnava 



