OBSERVATIONS ON THYONE BRIAREUS. 26/ 



it. Occasionally individuals were found which burrowed directly 

 into the sand without attaching themselves to any solid object. 

 The results of an experiment performed on July 25 are typical 

 of the other cases of burrowing observed. Four animals were 

 placed in aquarium jars containing sand and sea water. One indi- 

 vidual burrowed straight down into the sand and covered itself 

 in three hours ; another lay on top of the sand two hours and 

 then took four hours to burrow ; the third individual twisted about 

 on top for half an hour, then came in contact with the side of the 

 jar and burrowed into the sand in two hours and a half; the 

 fourth took four hours to reach the side and then partly covered 

 itself in two hours. On another occasion an animal lay on the 

 sand eighteen hours but covered itself in two hours when placed 

 against the side of the jar. 



Burrowing is accomplished by a contraction of the body muscles 

 and the action of the tube-feet. When the body is fastened to 

 some solid object, the tube-feet are attached as far down its side 

 as possible and the body is drawn out so that it is wedge-shaped 

 in cross-section. The longitudinal body muscles are then con- 

 tracted so that the body shortens, and the sand is forced aside 

 as the cross-section becomes more circular in outline. During 

 the entire process the two ends of the body are turned upward 

 and the animal sinks down into the sand with the dorsal surface 

 constantly uppermost. This method of procedure is usually re- 

 peated until the individual is completely buried, except the pos- 

 terior end. The downward movement is assisted by the passage 

 of constricted rings from one end of the body to the other, or 

 from both ends toward the middle, the sand thus being loosened 

 so that the body can be "wedged" down into it. When there 

 is no solid object for the attachment of the tube-feet, burrowing 

 is more difficult. As the waves of contraction pass over the body, 

 the sand is gradually pushed aside so that a thin portion of the 

 ventral surface is forced downward (Fig. 2, A). The dorsal longi- 

 tudinal muscle bands and the circular muscles then contract and 

 the ventral portion of the body expands in such a way that the 

 sand is forced aside (By This same process is repeated at inter- 

 vals until the animal is covered. 



Thyone can move about to some extent after it is buried in the 



