If we stopped to rest on the buttressed roots of some great cottonwood, we saw a few of the minor creatures whose existence is hardly suspected by the casual observer. What at first appeared to be a maze of cobwebs filling the entrance to a dark cavern under the roots, resolved into a moving, living mass. A closer inspection, and small, black specks could be distinguished in the madly weaving and revolving haze, and also long, threadlike legs dangling so idly that one wonders why they do not become hopelessly entangled with those of their neighbors. This peculiar, wavering flight of the crane-fly seems to form the delicate, spidery creature’s chief occupation, for I rarely found them at rest. Presently, other little insects, encouraged by the silence, make their appearance. First among them may be a small _Gastaracantha_ spider, slowly letting itself down from an overhead twig on a thread of finest gossamer. At first glance one may easily mistake the insect for a minute crab that has fallen from the leafage into a silken snare, but when, at the watcher’s first movement, it either runs nimbly up the dangling thread, or drops to the ground with a rapid slacking of line, one is convinced that it must be a spider. The hard shell, or back, is fringed with sharp, upturned spines and is of an orange color marked with a number of small black dots. After a shower, mosquitoes were numerous and attacked with the utmost persistency. This irresistible thirst for blood is very extraordinary; it does not seem possible that more than a very small proportion of the countless millions of these insects living in a given area ever have an opportunity for satiating their appetite for blood during their entire lifetime; yet the instinct remains, and they attack on sight ferociously and without hesitation any living thing whose skin their beaks can penetrate. It is also a well-known fact that malarial fever, so prevalent in the tropical lowlands, is transmitted by a genus of mosquito, _Anophiles_. The germ of this fever, however, passes only one period of its existence within the insect’s body, and the spores must be secured from some living creature, and after development transmitted to another to complete the life cycle. Some of the areas in which malaria abounds are practically uninhabited by human beings, so this agent in the propagation of the disease is of course lacking--at least to a considerable extent. It naturally follows, therefore, that some other creature or creatures, may be preyed upon and inoculated by _Anophiles_. I have on several occasions observed pet cebus and woolly monkeys (_Lagothrix_) that showed decided symptoms of suffering from malaria, and to me it seems highly possible that monkeys may be at least one of the animals that serve to keep the infection alive.