1 68 HYMENOPTERA CHAP. 



however, that some other function will be found to exist for 

 these forms with enormous heads. An examination of their 

 organs of sense and of voice is very desirable. 



Details of the modes in which the great communities of the 

 leaf- cutting Attidae are maintained, are still wanting. The 

 females do not, we have been informed by Mr. Hart, possess 

 any considerable powers of aftergrowth, so that there is no reason 

 to suppose them to be unusually prolific. At certain seasons 

 great swarms of winged individuals are produced, and after 

 leaving the nests pair in the manner of our European Myrmica. 

 Possibly the females may, after losing their wings, again enter 

 the large communities. Yon Ihering states that the workers of 



o o 



Atta lundi are fertile. 



iii. The group PSEUDOMYRMIXI includes the genera Pscudo- 

 ini/riiia and Himn, which are by some entomologists treated as 

 but a single genus. The antennae are inserted near together on the 

 front of the head ; there is no carina on the head external to 

 their insertion, and the clypeus does not extend forwards between 

 them. The Insects are usually of elongate form, possess a sting, 

 and have a naked pupa. The group occurs in both hemispheres, 

 but is exclusively exotic, and but little is known of the habits of 

 its members. Forel has recently observed that numerous species 

 live inside dried stems of grass or in hollow twigs, and are 

 beautifully adapted for this mode of life by their elongate form, 

 some of them being as slender as needles. Some interesting 

 observations have been made in Nicaragua by Belt on Pscudo- 

 mynna bicolor and its relations with an acacia-tree, in the thorns 

 of which it lives. The acacia in question is called the bull's-horn 

 thorn, because the branches and trunk are armed with strong 

 curved spines, set in pairs, and much resembling the horns of 

 the quadruped whose name they bear. The ant takes possession 

 of a thorn by boring a small hole near the distal extremity, and 

 forms its nest inside. The leaves of this plant are provided 

 with glands that secrete a honey-like fluid, which it appears 

 forms the chief, if not the sole, subsistence of the ant. I'.elt 

 considers that the presence of the ant is beneficial to the acacia ; 

 he supposes that the ants assume the rights of proprietors, and will 

 not allow caterpillars or leaf-cutting ants to meddle with their 

 property ; the leaves are, he thinks, so preserved to the benefit 

 of the tree. 



