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mass as are those of the other genera of Comasteridæ, in which 
the very young always have ten arms. 
We do not know how frequent are the breeding periods; they 
may be annual or semi-annual, or separated by more or less irre- 
gular intervals; neither do we know how long it takes a crinoid 
to attain its full size. It is probable that crinoids grow with 
considerable rapidity; the common West Indian sea-urchin, Hip- 
ponoé esculenta, appears to develop to edible (adult) size in about 
six months; it has been observed at Bårbados, where this urehin 
is of very considerable economic importance, that grounds completely 
fished out will be restocked with urchins of marketable size in 
approximately six months. This may mean two things; (1) that the 
larval urchins drifting in from outside grew to adults in six months, 
or (2) that small specimens, not marketable, were left, which in 
six months attained sufficient size to be of value; the former is, 
however, probably nearer the truth. 
Contrary to the conditions prevailing in regard to the Coma- 
steridæ, the Antedonidæ, the Zygometridæ, and the. Himerometridæ, 
thé Thalassometridæ are creatures of markedly solitary habit. I 
have seen the accumulator on the dredge of the ,,Albatross'' register 
at least four tons when the net contained practically nothing 
but Heliometra; but my greatest catch of any species of Tha- 
lassometridæ in any one haul was seven, and the usual number 
is one or two. Such a vast difference in habit necessarily means 
svme radical difference in something else; that something elsé is 
not far to seek; the Thalassometridæ have small eggs which, as 
the adults are on an average as large as those of the other families, 
presumably require a longer time for development; as the penta- 
crinoids are not much, when at all, smaller, we infer a somewhat 
longer pre-pentacrinoid or free-swimming stage. Now, as: I havé 
shown, a long free-swimming stage would mean a wide distribution 
both geographically and bathymetrically for species of this family, 
and we find that here facts accord with theory; moreover, the young 
would be far less likely to develop on or near the parent, but 
