LEPHX.) 5. Echinoderma, simple aquatic animals, for the most part provided with a calcified terior 'skeleton or a coriaceous skin, the body for the most part radiated, globular, or drical, often provided with a distinct nervous, muscular, respiratory, and vascular system. These animals have received the names of noderma, from the spines or tubercles which generally cover their exterior surface, as seen in the annexed figure of the echinus esculentus (fig. 33.) The mouth (b) is here in the centre of the lower surface, and the intestine (b,b.) connected to the shell by a mesentery (c), on which vessels are mified, passes in a convoluted manner upwards to the site axis where the anal aperture (a) is surrounded by the five openings of the ova ries (d,d.) The mouth is surrounded with a maxillary apparatus containing five teeth, and the exterior of the.
_________ cumplicated and solid shell is seen to be provided with moveable cal careous spines. These animals are for the most part free, but some are fixed, as the echinoderma, the vascular system is unpro vided with auricle, or ventricle, and the diges tive canal is seldom furnished with distinct glandular organs. There is sometimes a simple
stomach with one aperture and numerous late ral caeca., and sometimes a lengthened intestine with two terminal openings. Some marine animals without an echinodermatous covering are placed in this class from the similarity of their structure in their more essential organs, as is the case with the holothuria represented in fig. 34. The mouth (a) is here surrounded with • - ramose tenta cula (c) and an osseous ap paratus. The intestine is long, convolu ted, vascular, supported by a mesentery, and termi nates in a cloaca (i) at the opposite axis of the bo dy. The rami fied internal branchim (1f) open from the cloaca ; the great systemic artery receives the aerated blood from the branchire, and the organs of generation (m) open near the anterior part of the body. The irritable coriaceous skin is supported by five broad longitudinal subcutaneous muscular bands, and five crowded series of tubular mus cular. feet extend from its surface. (See Ecxx NODERMA.) The SECOND SUB-KINGDOM or DIPLO-NEU