122 Papers from the Department of Marine Biology. 



are essentially different from the other classes of echinoderms in either 

 the length or activity of their free-swimming life. 



Mr. Clark says of the young of starfishes and brittle-stars that their 

 occurrence in numbers at the surface of the sea " indicates a power of 

 dispersal quite unattainable by the crinoids." Here again we have a 

 pure assumption. Starfishes and brittle-stars are more or less abun- 

 dant in all regions where there are marine laboratories, and we know 

 something about the larvse and larval habits of a few species. Except 

 perhaps Misaki, there is not a permanent marine laboratory in the 

 world where more than a single species of crinoid is available for study, 

 and comatulids are common only in regions which have as yet been 

 hardly touched by the student of echinoderms. It is unreasonable to 

 base an argument on what we do not know. 



Further on in his paper (p. 603), Mr. Clark contrasts crinoids, 

 as " practically sessile" organisms, with sea-urchins, starfishes, and 

 brittle-stars. Judging wholly from my observations at Mae'r, where 

 more than 20 species of crinoids, 20 of starfishes, 50 of brittle-stars, 

 a dozen of sea-urchins, and 40 of holothurians were collected on the 

 reefs, I should say that echini are the most sedentary ("sessile") of the 

 five classes. Certainly nearly all echini, most holothurians, and many 

 starfishes are quite as inactive as the comatulids. Many echini and 

 some holothurians live in holes and crevices in rock which are appar- 

 ently prisons and from which they do not, and sometimes certainly 

 can not, move. I have never found a comatulid so situated. In this 

 connection it is appropriate to quote a paragraph from a letter written 

 by Dr. L. E. Griffin, formerly of the Bureau of Science, Manila: "I 

 saw in ' Science ' that you discovered crinoids swimming at Maer. One 

 I sent you from Culion was a very active swimmer and lived among 

 the eel-grass. We have often seen them swimming in the P. I." 



In reference to the food of crinoids, Mr. Clark says (pp. 603-604) 

 that "at or near the surface a crinoid must depend upon" small 

 pelagic organisms "which swim within reach of its pinnules or which 

 it may intercept with the slow motion of its arms." These words 

 seem to indicate that Mr. Clark looks upon the food as being captured 

 by the crinoid, whereas it appears to be simply a matter of passing 

 the sea-water, actually swarming with organisms too minute to be 

 individually captured, through the ciliated furrows to the mouth. 

 Mr. Clark goes on to say that "in deeper water," the crinoid would get, 

 in addition to this food supply, "all the carcasses" of the organisms 

 which die in the water above it. And he concludes: "The intensity of 

 this rain of food increases, of course, proportionately with the depth, so 

 that the deeper a crinoid lives the greater is the available food-supply ; 

 consequently, the better nourished is the individual and the greater 

 is its size." (In justice to Mr. Clark it should be added that he sets 

 600 fathoms as a limit beyond which this rainfall of dead organisms 

 would cease to be available for the crinoids.) 



