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 havea 
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 larve 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 Maér, 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 froma letter written 
by Dr. L. E. Griffin, formerly of the Bureau of Science, Manila: “I 
saw in ‘Science’ that you discovered crinoids swimming at Maér. 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 ecrinoids.) 
