. Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote. 298 ECIIIXODERMATA. A rows from the oral to the 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 anibulacral 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 with a suctorial disc: in other cases they are conical, and the suctorial
. Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote. 298 ECIIIXODERMATA. A rows from the oral to the 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 anibulacral 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 with 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 anibulacral appendages, are simple or pennate, or even dendritic (Dendrochirota) or shield-shaped (As2)idochirota}, that is, provided with a disc, which is often divided into many parts. In certain genera (Synapta), the ambulacra! feet are altogether wanting, and the tentacles re- main as the sole appendages of the anibulacral system (fig. 240). Locomotion is effected by the strongly developed dermal mus- cular system, the longitudinal fibres of which are attached to the calcareous ring surrounding the oesophagus. It is charay- teristic of the water-vascular system that the stone canal, which is usually simple, hangs freely in the body cavity, ending in a calcareous framework com- parable to the madreporic plate. The respiratory trees at the end of the intestine perform the func- tion of respiration, while certain glandular appendages (organs of Cuvier), which open into the rectum, may be regarded as excretory oryans: these, as well as the respiratory trees, may be wanting. The generative oryans consist of a bundle of branched tubes, the duct of which opens on the dorsal surface in the region of the mouth. The genus Synapta is hermaphrodite. The development is in many Holothurians direct (as in Hulothnria tremula according to Koren and Danielsscn); whe
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