first, owing to the superstition of the Norwegian sailors, who regard it as "bewitched." found on the northern shores of Britain. It is also Fig. 204. Female of Masked Crab (Corystes Cassivelaunus). The Crystal Palace Aquarium possesses living specimens of Euryonome aspersa, Hyas coarctus, Pirimela denticulata, Pilumnus hirtellus, as well as the "nut" crabs (Ebalia), and the "angled" crabs T (Gonoplax). The former has the singular habit when at rest of simulating the appearance of rounded quartz pebbles. In addition to these may also be seen the interesting Xantho florida and X. rivulosa, as Fig. 205. well as Dromia vulgaris, or "toad crab," so called from its sluggish appearance. It is covered with a kind of pile or hair. The fourth and fifth pairs of legs are very short, and close-pressed against the carapace. Several species of Mediterranean and American crustacea may also be seen alive in one or other of these tanks of our public aquaria. It is only within a few years that the very large and widely distributed family of marine animals known as "barnacles" (Cirripedia) have been proved to belong to the same order as crabs and lobsters, and therefore to be veritable crustaceans. Darwin's monograph of these interesting creatures has placed them in a new light. Unlike the evolution of many animals, which begin in a simple way, and gradually pass through embryonic stages to a more complex (as the lobster, for example), the barnacles are actually more highly organised when they are young, free-swimming, and crustacean-like, than when they have reached the adult condition. Their life-history is a retrogradation, zoologically speaking, in order the better to adapt them to the very peculiar habits of life which we find them affecting. We can group the Cirripedia into two natural divisions, stalked and sessile, of which the stalked barnacle (Lepas anatifera), and the sessile "acorn" barnacle, we find so uncomfortably covering seaside rocks, Fig. 206. are relative examples. The beauti- Sessile Acorn Barnacle ful plumes or gills protruded from the semi-opened calcareous valves of the former, are These constantly sweep the water in well known. search of fresh oxygen and food. When the stalked species (so called from the flexible muscular tube, often of great length, to the free end of which the body of the barnacle is attached) have ceased leading a free-swimming life, they in reality settle down by their heads. The feet then produce the feathery gills, and are hereafter employed in sweeping the water to and fro, instead of swimming or walking. In reality there is not much modification here, for if the legs of a lobster be plucked off sharply, there |