Chap. VI] ANIMALS 141 



ivhich lias 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 

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

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

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

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

 diblc objects, termed after their discoverer Belt's corpuscles, may, from 

 I morphological point of view, fairly be regarded as transformed glands, 

 rhey are however distinguished from all known glands by definite 

 ;haracters — larger size, longer duration, richness in proteids, easy severance 

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

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

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

 levelopment. A fact of special significance is that precisely similar 

 odies occur in the moraceous genus Cecropia and the acanthaceous 

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

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

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



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

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

 he South Brazilian C. adenopus. 

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

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

 .'idely distributed and common everywhere, in rain-forests as well as in 

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

 apociras of the Brazilians) which in rainy districts speedily cover abandoned 

 'lantations or restock ruined virgin forest. Their slender stems shoot 

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

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

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



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

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

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

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

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

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

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

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

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

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

 nd Hydnophytum, which will be described further on. 

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



