122 CONNECTICUT GEOL. AND NAT. HIST. SURVEY. [BuU. 



verging to a central tube, the genital duct. In reality these 

 filaments are in two clusters, one on each side of the mesentery, 

 but are commonly so closely interwoven as to appear as a single 

 cluster, as represented in Plate XXX. The genital duct passes 

 forward as a slender canal in the dorsal interradius. It opens to 

 the exterior in the mid-dorsal line between the bases of the dorsal 

 tentacles. A small papilla marks the opening of this duct in the 

 males. 



HABITS AND FOOD 



The holothurians are usually very sluggish in their move- 

 ments, although they respond suddenly and vigorously to various 

 stimuli. Our native species live largely in the mud or sand 

 between tides or on the sea bottom, moving slowly from place 

 to place as conditions of food or other circumstance may require. 



In the worm-like Synapta, locomotion is accomplished by the 

 contractions of tentacles and body walls, while the other species 

 are provided with very numerous pedicels or tube-feet by means 

 of which they can creep about. 



The species of Synapta live with the posterior end buried 

 deeply -in the sand or mud. In our other holothurians, however, 

 the cloacal opening is connected with the respiratory apparatus. 

 Hence in these species the body is usually bent into a U-shape 

 with both ends near the surface of the sand or mud in which the 

 animals live. 



Thyone. — The habits of the common Thyone and its response 

 to stimuli have recently been studied and described by Pearse.* 

 Very little is known regarding the natural history of Thyone 

 unisemita or Thyone scabra, for of these species very few speci- 

 mens have ever been seen alive. 



Living, active individuals of the common Thyone kept in an 

 aquarium are most interesting creatures to watch. The delicately 

 branched, purple oral tentacles (Plate XXXI) are constantly 

 being alternately stretched out and withdrawn, the finer branches 

 gliding over the materials on which the body is resting. If 

 imbedded in mud or sand the tentacles spread out widely explor- 

 ing the surface in all directions. By this means they come in 



"■Biological Bulletin, 1908, 



