Elementary text-book of zoology, general part and special part: protozoa to insecta . elementarytextbo00clau Year: 1892 298 ECIIIKODERMATA. rows from the oral to tlie anal pole, but may be principally or altogether confined to the three rays of the so-called trivium. In this latter case the Holothurid moves upon a more or less foot-like ventral surface. The ambulacral feet may also be distributed uni- formly over the surface of the body, especially on the ventral side. As a rule, the tube-feet have a cylindrical shape, and terminate -nith a suctorial disc: in other cases they are conical, and
Elementary text-book of zoology, general part and special part: protozoa to insecta . elementarytextbo00clau Year: 1892 298 ECIIIKODERMATA. rows from the oral to tlie anal pole, but may be principally or altogether confined to the three rays of the so-called trivium. In this latter case the Holothurid moves upon a more or less foot-like ventral surface. The ambulacral feet may also be distributed uni- formly over the surface of the body, especially on the ventral side. As a rule, the tube-feet have a cylindrical shape, and terminate -nith a suctorial disc: in other cases they are conical, and the suctorial disc is absent. The tentacles, which are in communication with the water-vascular system, and represent specially modified ambulacral appendages, are simple or pennate, or even dendritic (Dendrochirota) or shield-shaped (^Asjndochirota), that is, provided with a disc, which is often divided into many parts. In certain genera (Sijnajita), the ambulacral feet are altogether wanting, and the tentacles re- main as the sole appendages of the ambulacral system (fig. 240). Locomotion is effected by the strongly developed dermal mus- cular system, the longitudinal fibres of Avhich are attacked to the calcareous ring surrounding the oesophagus. It is charac- teristic of the water-vascidar system that the stone canal, which is usually simple, hangs freely in the body cavity, ending in a calcai-eous framework com- parable to the madreporic plate. The I'espiratory trees at the end of the intestine perform the func- tion of resjnration, while certain glandular appendages (organs of Cuvier), which open into the rectum, may be regarded as excretory orrjans: these, as well as the respiratory trees, may be wanting. The generative organs consist of a bundle of branched tubes, the duct of which opens on the dorsal surface in the region of the mouth. The genus Synajita is hermaphrodite. The development is in many Holothurians direct (as in Holotlmria tremula according to Koren
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