NO. 19.] ECHINODERMS OF CONNECTICUT. 115 



hard, spiny body coverings possessed by the starfish, brittle stars, 

 and sea-urchins, the holothurians have soft, sac-like or worm-like 

 bodies (Plates XXIX, XXXI, XXXII), in the skin of which 

 only very small calcareous plates are found. The mouth, at one 

 end of the elongated body, is surrounded by a circle of branched 

 oral tentacles comparable with the oral tube-feet or tentacles of 

 the other Echinodenns. The intestine ends in a sac-like cloaca 

 at the end of the body opposite the mouth. 



LV 



RV 



Fig. 20. Diagram of transverse 

 section of the body of a holothurian. 

 D, dorsal interradius ; I, I', I" , first, 

 second, and third sections of in- 

 testine attached to adjacent inter- 

 radii; LD, LV, RD, RV, and V, left 

 dorsal, left ventral, right dorsal, 

 right ventral, and ventral radii, res- 

 pectively. 



The body is in most species adapted for creeping upon the 

 sea bottom; and, as the animal habitually creeps with the same 

 side uppermost, there has come about a fairly well-marked dif- 

 ferentiation into a ventral and a dorsal surface. 



Three of the five ambulacral areas are situated upon the 

 ventral surface, and are usually provided with more highly 

 developed tube-feet, or pedicels, with sucking disks. The pedi- 

 cels of the two dorsal ambulacral areas are commonly modified as 

 delicate finger-like processes used for respiration and sensation. 

 In many forms, as Thyone (Plate XXXI), the pedicels are scat- 

 tered over the whole surface of the body, while in such burrowing 

 forms as Synapta there are no pedicels whatever (Plate XXIX, 

 figs. 1, 3). 



With the habit of creeping upon the side there has also come 

 a bilateral symmetry of the body, so that it is customary to speak 



