Amongst these Nauplii—all belonging to the great group Crustacea, which includes crabs and shrimps—is one which gives rise to an animal decidedly degenerate, but not precisely parasitic in its habits. This Nauplius is the young of the ship’s Barnacle, a curious stalked body, inclosed in a shell of many pieces (Fig. 9). The egg of the Barnacle gives rise to an actively swimming Nauplius, the history of which is very astonishing. After swimming about for a time the Barnacle’s Nauplius fixes its head against a piece of wood, and takes to a perfectly fixed, immobile state of life (Fig. 10). The upper figures represent the Nauplius stage of animals closely resembling the Barnacle: the lower figures show the transformation of the Nauplius into the young Barnacle. Its organs of touch and of sight atrophy, its legs lose their locomotor function, and are simply used for bringing floating particles to the orifice of the stomach; so that an eminent naturalist has compared one of these animals to a man standing on his head and kicking his food into his mouth. [Illustration: FIG. 9.—Adult Barnacle or Lepas (one of the Cirrhipedes). Natural size.] [Illustration: FIG. 10.—Development of Cirrhipedes (Barnacle and Sea-acorn). After Huxley.] Were it not for the recapitulative phases in the development of the Barnacle, we may doubt whether naturalists would _ever_ have guessed that it was a degenerate Crustacean. It was in fact for a long time regarded as quite remote from them, and placed among the snails and oysters; its true nature was only admitted when the young form was discovered. Other parasitic organisms, which exhibit extreme degeneration as compared with their free-living relatives, might be cited and figured in profusion, did our limits permit. Very noteworthy are the degenerate Spiders—the mites, leading to still more degenerate forms, the Linguatulæ. We have two of these represented in Figs. 11 and 12. The one (Fig. 11), as compared with a spider is seen still to possess the eight walking legs, small, it is true, whilst the palps and daggers of the spider have dwindled to a beak projecting from the front of the globular unjointed body. In the other the eight legs have become mere stumps, and the body is elongated like that of a worm. [Illustration: FIG. 11.—Acarus equi. A degenerate Spider or mite parasitic on the skin of the horse.] [Illustration: FIG. 12.—Degenerate Spider (Demodex foliculorum) found in the skin of the human face.]