260 



W. J. Crozier, 



geotropic irritability is also indicated by the fact, already referred 

 to, that Holothuria was found ventral side uppermost clinging to 

 the under faces of rocks. 



The presence of the nerve-ring is not essential for the climbing 

 of vertical walls. While regenerating new anterior ends the holo- 

 thurians were for the most part quiescent, but they occasinally 

 moved slowly about and were sometimes found to have crawled to 

 the water surface, assuming the position of normal individuals. 



3. Vibratory stimuli. 



Holothuria responded to slight jars of the table on which the 

 aquaria were placed by momentarily withdrawing the tentacles, and 

 ceasing the rhythmic cloacal movements. Tests were made by 

 placing holothurians in beakers of thin glass, three quarters filled 

 with sea-water, and tapping gently on the lip of the beaker. After 

 a certain number of repetitions of this stimulus, no response was 

 given. Table III gives, for ten experiments, the number of jars 

 required to bring about this state of accomodation ; the tapping was 

 done with a glass rod, the successive taps being one minute apart 

 and of as nearly equal force as possible. The extent of the reaction 

 obtained from different individuals was quite variable. Animals 

 designated b and h in the Table ceased to react, after giving the 

 number of responses noted, by withdrawing the tentacles permanently^ 

 the others by keeping them extended. While no withdrawing re- 

 flexes on the part of the tentacles were obtained after tapping for 

 some little time, continued jars induced restlessness and locomotion. 









Ta 



ble III. 











Exp. 46. 1,2 



Eeactions to jarring 



Individual 



No. of reactions 



a 



4 



b 

 2 



c 

 6 



d 

 9 



e f 

 6 3 



12 



h 

 3 



i 

 4 



J 



8 



Note. The "No. of reactions" given is the number reguired to bring about 

 accomodation in each case. 



Similar results were obtained by allowing drops of water to 

 fall from a height of 20 centimeters, approximately three centi- 

 meters of water being over the animals. The response here was 

 localized, the tentacles, mid-body region and posterior end all giving 



