Tired and hungry though we were, I was determined to put this story to the test; so Velasquez and I climbed up to the cliffs, and searched all round them, but could find no carving. At one place there was a large black stain on the cliff, produced by the trickling down of water from above, and I afterwards learnt that this stain at a distance somewhat resembled a bull, and a little imagination completed the likeness. The lady of the house where we stayed at Matagalpa assured us she had seen it, and that everything appertaining to a bull was there. This she insisted on with a minuteness of detail rather embarrassing to a fastidious auditor. Clambering down the rocks, we reached our horse and mule, and started off again, passing over dry weedy hills. One low tree, very characteristic of the dry savannahs, I have only incidentally mentioned before. It is a species of acacia, belonging to the section Gummiferae, with bi-pinnate leaves, growing to a height of fifteen or twenty feet. The branches and trunk are covered with strong curved spines, set in pairs, from which it receives the name of the bull's-horn thorn, they having a very strong resemblance to the horns of that quadruped. These thorns are hollow, and are tenanted by ants, that make a small hole for their entrance and exit near one end of the thorn, and also burrow through the partition that separates the two horns; so that the one entrance serves for both. Here they rear their young, and in the wet season every one of the thorns is tenanted; and hundreds of ants are to be seen running about, especially over the young leaves. If one of these be touched, or a branch shaken, the little ants (Pseudomyrma bicolor, Guer.) swarm out from the hollow thorns, and attack the aggressor with jaws and sting. They sting severely, raising a little white lump that does not disappear in less than twenty-four hours.