. Cassell's natural history. Animals; Animal behavior. NA TUBAL JUS a large Stiirfish dredged by the Challenger in the Soutliera Seas, a sort of tent is formed in the middle of the upper surface of the body, which consists of five membranous valves supported by spines. These valves can be raised or drawn together so as to form a low pyramid ; and the eggs pass directly from the ovaries into its cavity, where they assume the form of young Starfishes, without previously passing througli the Bipinnaria and Brachiolaria stages. In another species the spines covering the back have flattened
. Cassell's natural history. Animals; Animal behavior. NA TUBAL JUS a large Stiirfish dredged by the Challenger in the Soutliera Seas, a sort of tent is formed in the middle of the upper surface of the body, which consists of five membranous valves supported by spines. These valves can be raised or drawn together so as to form a low pyramid ; and the eggs pass directly from the ovaries into its cavity, where they assume the form of young Starfishes, without previously passing througli the Bipinnaria and Brachiolaria stages. In another species the spines covering the back have flattened heads, which tit closely together, so as to cover in the arcade-like spaces left between their shafts. The young develop within these spaces, eventually pushing their way out by 'forcing the ' spines aside. A similar nursery is formed on the back of a South ; Holothurian (Psolus) by the apposition of the heads of mushroom-shaped plates ; while in another species from the Falkland Islands there is no special nursery, but the young come to be packed into two continuous fringes adhering to the two rows of tube-feet along the back, which are imperfectly developed, and are not used for locomotion. In one South American Holothurian, however, the young are jirotected within the body of the mother, one individual having yielded sixteen j'oung measuring J-^ in length. In the viviparous Ophiurids, the nursery, though internal, is not a portion of the body-cavity, but a pouch which opens externally and projects into the body-cavity, serving also at the Ew same time as a breathing apparatus. There are usually ten of these â ^â â¢^ pouches, though as many as fourteen have been found in one individual^ each containing three young Brittle-stars. Echinoderms are to be found in all parts of the ocean, whether .,: in polar, tropical, or temperate regions, but they are most varied and. on the whole, most abundant in the shallower waters of the troijical le batliymetrical range, ex
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