no 



fleas. As the ant acacias seem at first sight to furnish even more 

 irrefutable arguments in favour of myrmecophily, I was glad to 

 have an opportunity during the winter of 1910-11 of studying 

 these plants in several localities in Panama and Guatemala. And 

 although my observations are not as complete as I could wish, 

 I believe they are not without interest, and I feel sure that my 

 sins of omission will be forgiven by any future investigator who 

 spends an equal number of hours in the fierce tropical sun and 

 submits to the fiery stings of an equal number of ants. 



It will be remembered that Belt (1874) studied the ant 

 acacias in Nicaragua. He found that the delicate, pinnate leaves 

 of these plants bear crateriform nectaries on their petioles and, 

 when young, also minute, bright yellow food-bodies at the tips 

 of their leaflets. He described and figured the huge stipular 

 thorns, which are paired and connate at the base. They are at 

 first filled with a sweet pulp, which is entirely eaten out of 

 both thorns by the ants, through a single opening made near the 

 tip of one of the thorns, and the smooth-walled cavit}^ thus pro- 

 duced is then used as a formicar}'. The ants explore the surfaces 

 of the leaves, collect the nectar and food-bodies, and in return 

 for these favours are supposed to protect the plant with their 

 stings from the attacks of herbivorous mammals, and especially 

 from the large leaf-cutting ants of the genus Atta. The acacia 

 ants which Belt observed were identified by Frederick Smith 

 as specimens of Pseudomyrma bicolor Guérin, which is synony- 

 mous \\dth Ps. gracilis Fabricius. Belt evidently believed that 

 the ants are in some way responsible for the peculiar enlarge- 

 ment of the thorns. 



We now know that the relation between the ants and the 

 acacias had been observed long before Belt's time. Hernandez 

 (1651) and Jacquin (1763) both noticed it in Mexico, and Com- 

 MELiN figured the food-bodies, or Beltian bodies, as they are now 

 called, as early as 1697, and Plukenet as early as 1720. Since 

 Belt's time the acacias have been studied in their native environ- 

 ment only by the Costa Rican naturaHst Anastasio Alfaro. 

 His observations, however, as reported by Emery (1891, 1892, 

 1894), are confined to notes on the various species of ants. All 

 other accounts, such as those of Commelin (1697), Beccari 

 (1884-86), Schimper (1888), and Rettig (1904), were based 



