688 Bulletin American M^tsenm of Natvral History. [Yo\. XXIII, 



but of zoological investigation, for closer inspection soon showed that the 

 ants are responsible for the inversion of the normal position of the strata. 

 It was the work of Atta sexdens. It is very doubtful whether such an 

 enormous task can be accomplished by any insects except the large species 

 of Atta." Von Ihering observed the marriage flight of A. sexdens and the 

 digging of the nests by the recently fertilized females, an instinct mani- 

 fested even by individuals whose gasters have been bitten off by birds. 

 A. sexdens extends southward in Brazil only to the Cebus-line (latitude 30°) 

 The nests of Acromyrmex lundi are excavated to a depth of 50-60 cm. 

 and consist of a single chamber with a cubic capacity of ^ to 1 litre, in older 

 nests 5 to 10 times as great. This cavity contains a single fungus garden 

 and is connected with the surface by means of a large horizontal or tortuous 

 gallery 1-2 m. long. From the nest-entrance, branching, well-worn roads 

 lead off over the surface often to a distance of 40 m. and further, and it is 

 along these that the ants travel to and from the grasses which they cut down 

 together with their green seeds. This ant carries the exhausted portions 

 of the fungus garden out of the nest and deposits them on a refuse heap. 

 The same is true of Mollerius striatus. This species clears the ground of 

 vegetation around its nest entrance which is surmounted by a crater. Like 

 A. lundi it collects pieces of grass, flowers, leaves, etc. A. niger nests in 

 thickets between the roots, where it excavates its nest at some distance 

 from the entrance. It does not confine its cutting operations largely to 

 grasses like bindi and striatus but attacks many other plants and is therefore 

 of greater economic importance. 



Cyphomyrmex morschi nests in the soil, where it excavates a chamber 

 about the size of an orange and containing a fungus garden of leaf detritus 

 covered with mycelium. The entrance is surmounted by a circular crater. 



Von Ihering is one of the few who have considered the question of the 

 origin of the fungus-raising instincts of the Attii. His remarks on this 

 subject will be considered in the concluding portion of this article. 



Uriah, in two papers published during the same year (1895a, 1895&) 

 records a number of observations on several of the Attii of Trinidad {Atta 

 sexdens, A. cephalotes, Acromyrmex octospinosus, Trachymyrmex urichi, 

 Sericomyrm£x opacus, Apterostigma urichi, A. mayri and Cyphomyrmex 

 rimosus). His account of the large species of Atta adds little of interest to 

 that of previous authors. On tAvo occasions he found the dealated females 

 of Acromyrmex octospinosus "working just as hard and engaged in the same 

 occupation as the neuters, viz: cutting leaves and carrying them to the nest. 

 They all issued from the same nest and therefore could not have been 

 mothers of new colonies." He "also noticed that several females lost their 

 wings in the nest without any marital flight, although a few weeks later the 

 winged ones swarmed out in the usual way on a damp evening." 



