Sensory reactions of Holothuria surinameusis. 259 



their re-attachment. Similar righting behavior was observed in 

 other species of Holothuria and in Siichopus. 



b) The climbing of vertical walls. All the holothurians 

 which I have studied were frequently found near the water surface, 

 on the vertical walls of aquaria in which they were confined. A 

 holothurian of different type, Cucumaria cucumis of the Bay of 

 Naples, supplied Loeb with a well known instance of negative 

 geotropism (Loeb, 1891), but Thtjone (Peaese, 1908, p. 275) does not 

 show any noticeable geotropic tendency. From the fact that (save 

 possibly in the case of Stichopus) crawling up a vertical surface did 

 not involve any orientation, I was led to believe that, with H. suri- 

 namensis at least, geotropic irritability was not necessarily the re- 

 sponsible factor. In crawling up the wall of an aquarium the long 

 axis of the animal was not placed vertically, but always at an 

 angle with the horizon, and the completion of the movement at 

 the surface of the water found the body placed horizontally imme- 

 diately under the surface film. Frequently the circlet of tentacles 

 was expanded and moved about under the surface film ; during this 

 manouver a few of the most posterior pedicels were' sufficient to 

 hold an animal in its position. Experiments were made with holo- 

 thurians placed upon glass plates tilted at an angle of 30° to the 

 horizon; in these tests approximately equal numbers crawled 

 upward and downward, while many remained stationary, the actual 

 figures being: 6 upward, 5 downward, 9 stationary in 20 tests. Not 

 all the specimens in an aquarium were at any one time to be found 

 on its sides; some came to rest in shaded corners and remained on 

 the bottom, while others crawled down from the water surface after 

 several hours. 



Jennings (1907, p. 115), Cowles (1910, 1911a), and Cole (1913a) 

 have called attention to the persistence of the impulse to locomotion 

 in starfish and ophuroids, and Cowles ascribes the climbing of 

 vertical walls by JEchinaster to this peculiarity of behavior. The 

 activity of Holotimria was very similar in this respect to that of 

 JEchinaster as described by Cowles (1911a), for, when oriented by 

 light or when engaged in continued locomotion from other causes, 

 this form also continued its crawling by mounting such vertical or 

 inclined surfaces as it met in its path. This was very noticeable 

 among animals freshly collected, for here the disturbance due to 

 handling and stimulation by light invariably resulted in the crowding 

 at the surface of all the holothurians in a pail. The absence of 



