708 SCIENTIFIC RECORD FOR 1883. 



attempt to turn itself, but when within two or thr, e minutes of its ces- 

 sation it commenced to do so. Moreover, if allowed to do so until it 

 had raised itself into the equatorial, or any other intermediate position, 

 if rotation was resumed, the sea-urchin remained in the position it had 

 then gained as long as it lasted. " Therefore no doubt could be enter- 

 tained that the effect of the rotation was that of confusing, as it were, 

 the co-ordinating influence of a nerve center, the stimulus to the opera- 

 tioB of which, in the absence of rotation, is gravity." (Journ. Linn. 800. 

 London, Zool, vol. xvn, pp. 131-137; J. R. M. S. (2), v. in, pp. 660-661.) 



Holothurians. 



The feeding of Holothurians. — The celebrated Darwin, in his work on 

 Coral Eeefs (p. 14), stated, on the authority of another, that the Holo- 

 thuriaus subsisted on living coral. The question has been lately 

 investigated, and an advance made in a knowledge of the economy of 

 those animals. Surgeon-Major H. B. Guppy, of the British navy, un- 

 dertook experiments at St. Christoval, one of the Solomon Islands, 

 which satisfied him that it was dead and not living coral that the Holo- 

 thurians ingested. They selected, however, "those -feeding grounds 

 where the attachment of molluscs, zoophytes, and stony algae had to 

 some degree loosened the surface of the rock." One of the Holothuriau 

 species which the surgeon studied was 12 to 15 inches long. From 

 three independent observations on this species it was found that the 

 amount of coral sand voided by each individual daily was not less than 

 two-fifths of a pound avoirdupois. "At this rate some fifteen or sixteen 

 of these animals would discharge a ton of sand from their intestinal 

 canals in the course of a year, which represents almost 18 cubic feet of 

 the coral rock forming the flat on which these creatures live." 



The raison d'etre and mode of ingestion of the Holothurians have been 

 explained by Mr. W. Saville Kent. That the Holothurians are not de- 

 vonrers of living corals is shown in connection with different facts, but 

 especially from the circumstance that several were kept in a tank con- 

 taining sea-anemones and corals without interfering with them in any 

 way. All they require is derived from the coral or shell debris with 

 which they are constantly associated. At first sight this material would 

 appear to be in the last degree adapted for the sustenance of such 

 highly organized animals, but, as may be confirmed at any time by in- 

 vestigation, "shell-sand, gravel, and other dSbris forming the super- 

 ficial layer at the bottom of the water, when exposed to the light, is 

 more or less completely invested with a thin pellicle of Infusoria, Dia- 

 toms, and other microscopic animal and vegetable growths." It is upon 

 these minute organisms that the Holothuriau feed, swallowing both them 

 and the shelly or other matter upon which they grow, much in the same 

 way as we might subsist on cherries, swallowing stones and all. 



It is by means of the tentacles which surround the anterior extremity 

 that the Holothurians seize their food. Cucuinariae of two kinds — C. com- 



