Chap. VI] ANIMALS 141 



which has been frequently the subject of subsequent nvestigations. Both 

 these acacias, and many other species besides, possess large, hollow, and 

 relatively thin-walled, stipular thorns that serve as dwelling-places for 

 a definite species of fierce ant, which bores an entrance-hole into them 

 near the tip. At the ends of the leaflets, but for the most part only in 

 the upper half of the leaf, there are found small ovoid or pear-shaped 

 structures, which are industriously collected and eaten by the ants. These 

 edible objects, termed after their discoverer Belts corpuscles, may, from 

 a morphological point of view, fairly be regarded as transformed glands. 

 They are however distinguished from all known glands by definite 

 characters — larger size, longer duration, richness in proteids, easy severance 

 when touched — all of which features may, with as much certainty as is 

 possible in such cases, be regarded as adaptations to ants. In addition, 

 they have no secretory power, at least during the later stages of their 

 development. A fact of special significance is that precisely similar 

 bodies occur in the moraceous genus Cecropia and the acanthaceous 

 genus Thunbergia, and are likewise associated with protective ants. The 

 like has never been observed in other plants. Moreover, a nectary situated 

 at the base of the petiole affords a liquid rich in sugar. 



Of all myrmecophytes, none have hitherto been so thoroughly investi- 

 gated in all respects as some species of the genus Cecropia, especially 

 the South Brazilian C. adenopus. 



The species of Cecropia (trumpet trees, bois canot, pao de imbauba) 

 are among the most conspicuous trees in tropical America. They are 

 widely distributed and common everywhere, in rain-forests as well as in 

 the thin forest strips of the xerophilous districts, and in the young woods 

 (capociras of the Brazilians) which in rainy districts speedily cover abandoned 

 plantations or restock ruined virgin forest. Their slender stems shoot 

 up everywhere like candelabra, supported on short prop-roots, and 

 divide above into boughs that are simply or scarcely branched. Their 

 large palmately lobed leaves occur only at the ends of the branches. 



A few active ants are always running along the branches and petioles 

 of Cecropia adenopus. If however the tree be somewhat roughly shaken, 

 then from minute holes in the stem and twigs an army of ants rushes 

 out and savagely attacks the disturber. In Santa Catharina, it is always 

 the same species of ant, Azteca instabilis, and the species apparently 

 occurs only on Cecropia. It is one of the most bellicose ants that 

 I know, and its sting is most irritating. In both these ways it surpasses 

 all the ants that I became acquainted with as inhabitants of other plants, 

 and even, in spite of the possibly exaggerated accounts of travellers, the 

 ants of the ' living ants' nests ' of the Malayan Archipelago, Myrmecodia 

 and Hydnophytum, which will be described further on. 



The most formidable foes of the imbauba-tree are the leaf-cutting 



