A treatise on zoology . eached, it will be useful to recapitu-late here the common pelmatozoic characters as well as thosedistinctive of the Crinoidea, as manifested in a normal crinoid ofsimple structure. The specialisation of those characters will beshown historically in the systematic part; but since manystructures have been produced or modified in the same way morethan once, a general account of the processes may be given can speak more decidedly on questions of development andinternal anatomy in this class, since the differences between extinctand recent genera are not such as to
A treatise on zoology . eached, it will be useful to recapitu-late here the common pelmatozoic characters as well as thosedistinctive of the Crinoidea, as manifested in a normal crinoid ofsimple structure. The specialisation of those characters will beshown historically in the systematic part; but since manystructures have been produced or modified in the same way morethan once, a general account of the processes may be given can speak more decidedly on questions of development andinternal anatomy in this class, since the differences between extinctand recent genera are not such as to hinder interpretation. A normal Crinoid was thus described in 1821 by J. S. Miller,the founder of the class : An animal with a round, oval, orangular column, composed of numerous articulating joints,supporting at its summit a series of plates or joints forming a 7 98 THE CRINOIDEA cup-like body containing the viscera, from whose upper rimproceed five articulated arms, dividing into tentaculated fingers, ^ndl Xvibe innuL. A simple form of Crinoid : Botryo-crinus decadactylus of the WenlockLimestone, seen from posterior inter-radius. more or less nunieruus, surrounding the aperture of the mouth,situated in the centre of u j)lated integument, which extends overthe abdominal cavity, and is capable of being contracted into aconic or proboscal shape. Some species of these animals ascer- 77/A CRINOIDEA 99 tained to be permanently attacherl to extraneous })0(lies, whilstothers ap})ear to liave been capable of loconiolion. So little isamiss with this description, that we need do no more than trans-late it into modern terminology, as follows :— A normal Crinoid (Fi^. III.) consists of a crowt) (rorona)attached by its dorsal { aboral) exi rcniity to a * stem {colarana),which is fixed to the sea-Hoor or to some solid body by a root{radix). The crown consists of a fJieca (or calyx, in the senseof Wachsniuth ^ Sj)ringer) containing the viscera, and of 5 arms (hrachia), which may be mor
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