The barnacles have, in fact, undergone a transformation which may be compared to that experienced by a man who should begin life as an active boy running about as others do, but be compelled suddenly by some strange spell or Arabian djin to become glued by the top of his head to the pavement, and to spend his time in kicking his food into his mouth with his legs. Such is the fate of the barnacles, and it is as strange and exceptional amongst crustaceans as it would be amongst men. Indeed, to "earn a living" human acrobats will submit to something very much like it. It is this change from the life of a free-living shrimp to that of a living lump, adherent by its head to rocks or floating logs, that Vaughan Thompson in 1830 discovered to be the story of every barnacle, and so showed that they were really good crustaceans gone wrong, and not molluscs. It is a curious fact that the young ascidian or sea-squirt which swims freely and has the shape of a tadpole, also when very young fixes itself by the top of its head to a rock or piece of seaweed, and remains immovable for the rest of its life. Though agreeing in their strange fixation by the head, the barnacle and the ascidian are very different kinds of animals. (For some account of the Ascidian the reader may consult the chapter "Tadpoles of the Sea" in "Science from an Easy Chair," Second Series. Methuen, 1912.) The name "Cirripedes" is commonly used for the order or group formed by the barnacles--in allusion to the plume-like appearance of their "raking" legs. Stalked barnacles often are found in the ocean attached to floating pumice-stone, and one species has been discovered attached to the web of the foot of a sea-bird. They, like many other creatures, benefit by being carried far and wide by floating objects. Whales have very large and solid acorn-barnacles peculiar to them, fixed deeply in their skin. Others attach themselves to marine turtles. With few exceptions the crustaceans are of separate sexes, male and female. But in nearly all classes of animals we find some kinds, even whole orders, in which the ovaries and spermaries are present in one and the same individual. "Monœcious" or "one-housed"--that is to say, possessing one house or individual for both ovaries and spermaries--is the proper word for this condition, but a usual term for it is "hermaphrodite." "Diœcious" is the term applied to animals or plants in which there are two kinds of individuals--one to carry the spermaries, the male, and the other to carry the ovaries, the female. It is probable that the monœcious condition has preceded the diœcious in all but unicellular animals. In vertebrate animals as high as the frogs and the toads we find rudimentary ovaries in the male, and in individual cases both ovaries and spermaries are well developed. Such a condition is not rare as an individual abnormality in fishes. In some common species of sea-perch (Serranus) and others it is not an exception but the rule.