In crabs the cephalothorax is depressed and often broader than long. The abdomen is relatively small and is folded under the thorax, lying in a groove which it fits so perfectly as to be quite hidden from above. The appendages of the abdomen are much reduced in number. The male has two pairs; the female has four pairs, which it uses for carrying its eggs. The first pair of walking-legs are comparatively large, and end in chelæ, or pinching-claws. The other eight legs terminate in simple points, except in the swimming varieties, when the fifth pair is flattened to form fins, or swimming-paddles. The eye-stalks are long and fit into sockets on the carapace. Both pairs of feelers are small. The antennules are frequently folded into small grooves. The external or third pair of maxillipeds are broad and flat, and cover the mouth-parts like a lid, or operculum. [pg273] Crabs, like other crustaceans, are scavengers, living on dead animal matter; but the land species are also vegetarian in diet. They are great fighters, but are also wily, often averting danger by resorting to stratagem. They are an interesting and curious group, as they possess a good degree of intelligence and have amusing habits. From the time they leave the egg until they attain the adult form they pass through several complete and singular metamorphoses. The most marked forms are called the /Zoëa/ and the /Megalops/. So little do these resemble the adult that originally they were classed as distinct genera far removed from the one to which they really belong. After the larva has moulted several times it appears as in the illustration on page 248—the last zoëa stage. From this it changes directly to /Megalops/; the /Zoëa/, seeming to be attacked with violent convulsions, wriggles out of its skin a full /Megalops/ (page 248). The animal then has enormous eyes, an extended abdomen, an elongated carapace, and swimming-legs. This stage is a short one, and at the first moulting changes to a form nearly approaching the adult. From this time they grow by shedding the shell at certain periods. This shedding is supposed to occur twice each summer until they have reached full growth, after which it is probable that they do not again moult; for often they are found with extraneous organisms, such as barnacles and sponges, upon them, of a size that must have required a considerable period of time for growth. The sexes of the same species sometimes differ so much that it is difficult to classify them. Even naturalists have been led into the error of assigning the male and female to separate species.