124 Papers from the Department of Marine Biology. 



Mr. Clark says (p. 606) that very large species of " Comasteridae 

 occur abundantly in very shallow water, often just below the low-tide 

 mark" in the tropics. This is apparently true for Maer, though it is 

 not clear what Mr. Clark would call "very large." But when he says 

 that the individuals "decrease in size with depth," doubt may well 

 be felt. Of course, when a depth sufficient to diminish the amount of 

 vegetable plankton is reached comatulids very possibly become fewer 

 and smaller. No crinoids were taken at Maer at a depth sufficient to 

 throw any light on this point. It is certainly true at Maer, as Mr. 

 Clark goes on to say, that "the beaches and rocky shores warm up, to 

 be covered again at high tide with comparatively cool water full of 

 organisms," but when he adds the words "unable to stand a great 

 change of temperature," we may well ask for evidence. On the reef 

 flats at Maer we found that many organisms living in the area where at 

 low tide the water became heated were able to thrive within wide limits 

 of temperature. Moreover, as the cold water of the incoming tide 

 comes over the flat, it is not appreciably raised in temperature, but 

 brings down to its own degree the water, rocks, and sand which have 

 been heated. There was never the least evidence of the destruction of 

 pelagic life on the reef flat due to heat. But even granting that such 

 a destruction does occur, why should Mr. Clark say it would be "swept 

 back into the sea, to fall just beyond the low-tide mark?" Would it 

 not be just as probably washed up on the beach, dropped on the reef- 

 flat, or carried far out to sea by the receding tide, as deposited just 

 below low-tide mark? 



In conclusion, on this subject of the food of crinoids, the legitimate 

 criticism of Mr. Clark's views may be summed up in this way: While 

 there need be no quarrel with his assumption that a big food-supply 

 will give rise to big crinoids, as there certainly is such a factor in the 

 growth of some species of starfish, it must not be forgotten that it is 

 after all only an assumption. When to this he adds the assumption 

 that animal food, especially in the form of a hypothetical "rainfall of 

 carcasses," is the fundamental factor in accounting for the distribution 

 of big crinoids, we may well become exceedingly skeptical, since the 

 evidence obtained at Maer shows that the comatulids are vegetable 

 feeders, and live in such positions that no "rainfall" of food could 

 readily reach them. Finally, the assumptions, by which he attempts 

 to account for the existence of the hypothetical "rainfall of carcasses" 

 in the various regions where the size of the crinoids seems to require 

 it, appear to be as dubious as they are ingenious. While fully recog- 

 nizing how limited our knowledge of crinoids is, we are obliged to 

 maintain that there are few facts known which give any support to 

 Mr. Clark's conclusions. 



In his discussion of the colors of crinoids, Mr. Clark has a much 

 better basis of fact, but here too he makes certain assumptions that 



