NO. 19.] ECHINODERMS OF CONNECTICUT. 121 



system. Both oral tentacles (Fig. 21) and pedicels are pro- 

 vided with muscular ampullae, which receive the fluid when the 

 pedicel or tentacle is contracted, as in the starfish. 



In Synapta, in which pedicels are wanting, the water-vascular 

 system is very rudimentary, and no radial canals occur, the ten- 

 tacles being connected with the ring canal. 



Musculature. — Paired bands of powerful longitudinal mus- 

 cles extend the length of the body in each of the five radii, while 

 transverse, or circular, muscles extend between the adjacent 

 radii. In all except Synapta the circular muscles are interrupted 

 at the radii. 



Attached to the calcareous ring are powerful retractor mus- 

 cles by means of which the crown of tentacles, and in fact the 

 whole anterior part of the body, can be completely withdrawn. 

 They are connected with the five pairs of longitudinal muscles well 

 back toward the middle of the body (Plate XXX). In some 

 specimens these retractors are split for the greater portion of 

 their length into pairs, corresponding with those of the longi- 

 tudinal muscles, but in other individuals the two parts of each 

 muscle are firmly united. 



The musculature of the cloaca is described above. 



Body Walls. — In this species the walls of the body are so 

 thick, tough and leathery that calcareous plates are wanting 

 except at the anterior and posterior ends of the body. In all 

 our other holothurians, however, characteristic plates are found 

 in all parts of the walls. These plates, as well as those that are 

 found in the tentacles and pedicels, are described in detail in 

 the descriptions of the different species, for they are in each 

 species of such characteristic form that they furnish the most 

 reliable means of recognizing specific differences. 



Nervous System. — The quick and vigorous response which 

 the animal makes to various stimuli indicates a highly sensitive 

 nervous system. 



In its morphological structure, however, the nervous system, 

 with its nerve ring and radial nerves, is closely similar to that 

 described for the starfish. 



Reproductive Organs. — The sexes are separate. The sexual 

 gland is attached to the dorsal mesentery, and consists of a brush- 

 like structure, composed of numerous slender filaments all con- 



