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might say usually, present upon the arms and pinnules of individuals 
belonging to the species of the other families, often in astonishing 
numbers; I have removed no less than ninety-three from the arms 
of a single specimen of Tropiometra afra. 
It is a very interesting fact that the forms with small eggs 
all, so far as we know, have pentacrinoids with short stems, com- 
posed of comparatively few short joints; thus they would be ill 
adapted to struggle with crowded conditions; while the pentacrinoids 
of species with large eggs have long stems composed of numerous 
greatly elongated joints, which enable them more successfully to 
contend with the crowded conditions of existence under which all 
the large egged species live. 
The ten-armed condition is undoubtedly the primitive condition 
of the comatulids"), and the species in the closely related family 
Pentacrinitidæ, and the young of multibrachiate species, with but 
few exceptions, are of this type. Now these ten-armed young 
have arms very much longer in proportion to the size of the disk 
than do the adults, so that the available food collecting area is 
proportionately just as great, if not greater. The multibrachiate 
species are essentially inhabitants of the more or less disturbed 
waters along the shore lines, and live under conditions where length 
of arm is a distinct disadvantage, owing to the economic loss due 
to constant fracture from being swept against and caught by 
surrounding objects as a result of the more or less constant wave 
motion. Probably the assumption of the multibrachiate condition 
was at first fortuitous, as it is now in the case of Antedon bifida 
and Comatula pectinata and in most of the Thalassometrinæ; but 
nature was quick to take advantage of it, and to carry it to extra- 
ordinary extremes. By a multiplication of the arms (and with 
them pinnules) the amount of ambulacral surface necessary to sustain 
life can be condensed into a circle of minimum diameter, making 
the animal far less liable to serious injury than if it expanded to 
Except in the family Pentametrocrinidæ. 
