NO. I. ECHINODERMS OF CONNECTICUT. 



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 Echinoderms. The intestine ends in a sac-like cloaca 

 at the end of the body opposite the mouth. 



RD 



LV--(- 



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 Thy one (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- i, 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 



