Sensory reactions of Holothuria surinamensis. 239 



of the tide, which at low water may expose to the bottom the direct 

 action of the sun; the matter is further complicated by the fact 

 that, at the shore line, cool water seeping from the porous limestone 

 tends to lower the temperature in certain spots. 



c) Feeding. Food ingestion is accomplished by Holothuria 

 with the aid of the tentacles, which, like the buccal pedicels of 

 spatangoids and ophiuroids (Grave, 1902, Horntold, 1909), shovel 

 loose bottom material into the mouth (cf. Semper, 1868, p. 103). 

 The large doubly flexed intestine is always full of sand, which 

 contains numbers of Foraminifera (Or&^cwZma, etc.) and other minute 

 forms, small mollusks and bits of shell. After the abstraction of 

 nutritive materials from the ingested sand, the inert residue is 

 passed out through the cloaca in a state of fine sudivision.^) This is 

 a matter of some geological importance, as there is good ground 

 for believing that through their mode of feeding holothurians play 

 an important role in the secondary decomposition of coral formations, 

 as has been brought out especially by the work of Gardiner (1903, 

 pp. 333—341). 



In the Cucumariidae there is a characteristic system of feeding 

 reflexes, which involves (Dohrn, 1875, Grave, 1902, Pearse, 1908) 

 the waving of the tentacles through the water or over the bottom, 

 and their consecutive cleaning by being wiped oö" in the mouth; 

 certain tentacles, in Thyone the two short ventral ones, are used 

 more frequently than the others. No preferential use of particular 

 tentacles was noticeable in Holothuria surinamensis. 



d)Eespi,rator3^ movements. In laboratory aquaria the 

 respiratory movements of the cloacal aperture occurred with conside- 

 rable regularity, at the rate of 1 min. 10 secs, for ten pulsations at 

 27°. These movements are essentially similar to those carried out 

 by Thyone (Pearse, 1908, p. 271), Caudina (Gerould, 1898) and 

 other holothurians, and need not be described in detail. The 

 rhythmic opening and closing of the cloacal brim is interrupted at 

 irregular intervals, either by a more powerful inspiration, or by a 

 complete closure of the orifice, which may persist for some minutes; 

 such interruptions occurred usually in company with spontaneous 

 contractions of the anterior end and retraction of the tentacles. 

 During "respiration" the time occupied by the open phase exceeds 



1) The literature dealing with the processes of nutrition in holo- 

 thurians is summarized by Jordan, 1913, Vol. 1, p. 257 — 266. 



