264 A. S. PEARSE. 



4. Change in Size. — As has been previously stated, this species 

 undergoes marked changes in size and may shrink to a half or a 

 third of its original volume when it is strongly stimulated. 



5. Feeding. — Under certain conditions the circum-oral tenta- 

 cles are extended and either waved in the water or swept over 

 the surface of the mud in which the animal is buried. They are 

 then consecutively poked into the mouth and wiped off. This 

 reaction has been briefly described by Grave (:02). 



6. Change in Respiratory Movements. — Water is periodically 

 drawn through the cloacal chamber into the respiratory trees and 

 expelled again. This series of breathing movements may be 

 interrupted for a time or the rate may be increased or decreased. 



7. Self Mutilation. — When the water becomes stagnant or 

 when conditions become otherwise unfavorable the anterior end 

 of the body is often cast off together with some of the visceral 

 organs. The lantern, the circum-oral nerve and water vascular 

 rings, the tentacles, and more or less of the enteric canal are fre- 

 quently lost in this manner. 



There are then at least seven well-defined reactions which may 



be used as a basis for the study of the behavior of Thyone. 



None of these responses are invariably called forth, however, 



when an individual is subjected to a certain stimulus. While 



one reaction is taking place it may exert an inhibitory influence 



on others, and the responses are all more or less changeable 



and therefore apt to vary in degree with a repetition of the same 



stimulus. 



IV. Locomotion. 



I. On a Solid Surface. — Individuals which were moving on 

 a solid surface were never observed to extend the tentacles and 

 remained more or less contracted so that they were usually not 

 more than seven or eight centimeters long. When an animal is 

 placed on the bottom of a dish in sea water it remains contracted 

 for a short time, but the ventral tube-feet usually become attached 

 within a minute. The posterior end is then slowly extended and 

 the respiratory movements begin ; the tube feet are protruded on all 

 sides of the body and begin to wave about, and those which come 

 in contact with a solid object attach themselves. The animal 

 may move in any direction but the locomotion usually carries 



