Jelly-fishes are often called “sea-nettles,” because of the microscopic poison-bearing threads which they discharge from their skin. These are used to paralyse their prey, and, in a few kinds only, are sufficiently powerful to cause a “stinging” effect when they come into contact with a bather’s skin. Sea-anemones are also armed with these minute threads, and their poison has been extracted and studied. The spines of star-fishes and sea-urchins have a very deadly poison associated with them, which has recently been examined. Among insects we have the bees, wasps, and ants, with their terminal stings; caterpillars, with poisonous hairs; gnats, with poisonous mouth glands. Residents in mosquito-infested countries become “immune” to the poison of gnat-bite, but not to the deadly germs of malaria and yellow fever carried by the gnats. The centipedes have powerful jaws, provided with poison-sacs; the spiders have stabbing claws, fitted with poison-glands. Shell-fish, such as crabs and lobsters, do not possess stings or poison-sacs, but some of the whelk-like sea-snails have poison-glands, which secrete a fluid deadly to other shell-fish. We have already spoken of the poison-spines of fishes; among reptiles it is only some of the snakes which are poisonous, and are known to have poison-glands connected with grooved fangs. Only one kind of lizard—the Heloderm of North America, already mentioned—has poison-glands in its mouth, but it has no special poison-fangs, only small teeth. There is a most persistent and curious popular error to the effect that the rapidly moving bifid tongue of snakes and lizards is a “sting.” It is really quite innocuous. No sting is known among birds, although some have fighting “spurs” on the leg, and “claws” on the wing. Only the lowest of the mammals or warm-blooded hairy quadrupeds—namely, the Australian duck-mole (_Ornithorhynchus_) and the spiny ant-eater (_Echidna_)—have poison-glands and related “spurs,” or stings. They have on the hind-leg a “spur” of great size and strength, which is perforated and connected with a gland which produces a poisonous milky fluid. Recent observations, however, as to the poisonous character of this fluid are wanting. Many mammals have large sac-like glands, which open by definite apertures, in some cases between the toes, in others upon the legs, at the side or back of the head (the elephant), in the middle of the back or about the tail. The fluid secreted by these glands is not poisonous nor acrid, but odoriferous, and seems to serve to attract the individuals of a species to one another. They resemble in structure and often in position the poison-glands of the spurs of the duck-mole and spiny ant-eater.