124 



by the daughters of these queens moving into thorns on the 

 same tree as fast as these became suitable as dwelhngs. That 

 different colonies of the same species of Pseudomyrma ma\- thus 

 readily coalesce is also indicated by the fact that these ants so 

 readily tolerate the presence of certain other distantly related 

 species on the same tree, as I shall now proceed to show. 



The Cases of Parabiosis. 



It is usually supposed that only one species of ant occurs 

 on an acacia tree, but we have seen that Alfaro on one occasion 

 found both Ps. belti and suhtillissima living side by side, and this 

 observer also found a second ant, Camponotus planatus, on trees 

 inhabited by the Pseudomyrmas. Emery's account of these 

 observations is not altogether clear. He seems to imply that 

 the Camponotus is merely a " Raumparasit," or inquiline of the 

 Pseudomyrma, and that it prefers to occupy the thorns of the dry 

 or dead branches. C. planatus is, according to my own observa- 

 tions, one of the most abundant neotropical ants, and has much 

 the same distribution as Ps. gracilis. Like this ant it usually 

 nests in the hollow twigs of a great variety of trees and bushes. 

 It is timid and very rapid in its movements, and in its foraging 

 and feeding habits resembles the other small arboreal species 

 of the huge genus Camponotus. I was surprised, therefore, to 

 find this ant on a large proportion of the Hving A. cornigera and 

 hindsii bushes at Escuintla, Patulul, and Quirigua, in company 

 with Ps. fulvescens, which it resembles in colour though not in 

 form. I was still more surprised to find it associated in the same 

 manner with the large black Ps. gracilis at Quirigua, where this 

 ant has become a common acacia tenant. In all of these locali- 

 ties and, as I have said, in many of the trees, a large number of 

 the thorns were occupied by C. planatus. And these thorns were 

 on the same twigs and branches as those occupied by Ps. ful- 

 vescens. The thorns containing the Camponotus are easily recog- 

 nisable, for they have larger openings because the bod}^ of this 

 ant, though shorter, is stouter than that of the Pseudomyrma. 



That the Camponotus does not, as Emery supposed, merely 

 take possession of thorns excavated and abandoned b}' the 

 Pseudomyrma, was proved on one occasion when I found a small 



