BOTTOM MATERIAL INGESTED — HOLOTHURIANS 387 



places, something like G.8 kilos (dry weight) per square meter 

 per year is eaten by Stichopus. The amount really concerned 

 cannot very well be much less ; it may be one and one half to two 

 times as great. 



If we attempt to figure the weight of bottom material eaten 

 by Stichopus in one of the partially enclosed sounds at Bermuda, 

 such as Harrington Sound, which has a superficial area of about 

 1.7 square miles, we find that probably not less than 500,000 kilos, 

 or say between 500 and 1000 tons, of bottom substance passes 

 through the intestine of this holothurian each year. This cal- 

 culation, necessarily of a rough order, is based on the assumption 

 that Stichopus is about as frequent in Harrington Sound as in the 

 average of places listed in table 1, and that the holothurians eat 

 but twice each day; these assumptions are admittedly rough, but 

 their respective inadequacies probably tend to counteract each 

 other. 



IV. The geological importance of the feeding activities of 

 Stichopus is determined by the magnitude of the changes which 

 may be produced by any or all of the following influences: 1) 

 in moving about, the holothurians may carry from place to place 

 some portion of the bottom deposits; as subsequently liberated 

 in castings, the ingested material may thus be carried near 

 to the water surface, exposed to wave action, and redistributed 

 over a new section of the bottom; 2) the mutual attrition of 

 calcareous fragments, especially when the ingested mass is under- 

 going segmentation in the intestine, may produce in a mechanical 

 way particles of a fine degree of subdivision; 3) the intestinal 

 fluids may dissolve part of the calcareous material ; if subsequently 

 precipitated in flocculent form, upon being expelled into the sea, 

 this material would assist in the accumulation of ooze. 



The first of these three factors is undoubtedly of some conse- 

 quence. The castings are readily broken up by currents, even 

 at a depth of several fathoms. The mucus which surrounds and 

 impregnates the ejected mass may have an action, as a protective 

 colloid, in assisting the dispersal of the finer particles by the 

 water, but this action can only be of a brief and temporary char- 

 acter, since the slime is soluble in sea water. 



