The weather was cloudy, threatening one of those cloudbursts during which some 1 to 1. inches of rain may fall in a day. The sun shone on the tree-tops and, although we were not exposed to the rays, the heat was asphyxiating. Thunder rolled at a distance. The clouds hovered over the peaks of the high Guàcharo chain, and the plaintive howling of the araguatoes, heard so often in Caripe at sunset, announced the imminent storm. For the first time we had an opportunity to see those howler monkeys that belong to the family Alouatta (Stentor, Geoffroy), whose different species have long been confused by zoologists close at hand. While the small American sapajous, who imitate sparrow song with a whistle, have a simple, thin tongue bone, the large monkeys, the alouates and spider monkeys (Ateles, Geoffroy), have a tongue that rests on a large bony drum. The sad howling typical of the araguato is produced by air penetrating violently into this drum. I sketched these organs (59) on the spot as they are not well known to European anatomists. If you think about the size of the alouatta's bony box and the number of howler monkeys that can gather in one tree in the Cumanà and Guianan jungles, you will be less surprised by the force and volume of their united voices.