OBSERVATIONS ON THYONE BRIAREUS. 2/3 



for by the fact that the movements which force the water into the 

 respiratory trees were more forcible after the period passed with- 

 out respiration and hence they required a longer time. In addi- 

 tion to the respiratory movements described there is doubtless 

 an exchange of gases through the integument and Thyone could 

 probably exist for some little time without spouting. 



VII. Responses to Stimulation. 

 Having completed the consideration of locomotion, feeding, 

 and respiration, attention will now be directed toward some of 

 the responses which result from such forms of stimulation as can 

 be controlled by the experimenter. 



1. Tactile Stimulation. — TJiyone is extremely sensitive to con- 

 tact with solid objects. If an animal is twisting about on the 

 surface of the sand and comes in contact with a solid surface, the 

 tube-feet are immediately extended and attached. Furthermore, 

 if an individual is placed in a glass dish, it comes to rest in the 

 angle between the bottom and side, where the body has the 

 greatest surface in contact. When the contact stimulus is received 

 from a moving object, the characteristic withdrawing reaction is 

 given and the response varies with the stimulus. The tip of a 

 glass rod may be gently pressed against the side of an individual 

 if the movement is very gradual but the same pressure will cause 

 a marked response if suddenly applied. The following experi- 

 ment is a good example of sensitiveness to jars and other slight 

 disturbances. A drop of water was allowed to fall from a height 

 of one meter into a one-liter beaker containing a feeding individ- 

 ual. As soon as the drop struck the surface of the water above 

 the animal, the tentacles were withdrawn and the cloacal opening 

 was closed. 



There is great variability in the sensitiveness of different indi- 

 viduals and those which had been in the laboratory for some time 

 often allowed the tentacles to be touched with a glass rod where- 

 as freshly collected individuals would contract at any slight jar, 

 such as the closing of a door. Grave (:05) obtained similar re- 

 sults from his study of Cucjnnaria. 



2. Gravity. — Thyone' s responses to gravity were tested in two 

 ways, by the righting reaction and by locomotion on an inclined 



