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one of the least pleasures that an admirer of comparative anatomy enjoys, 

 when he finds that results which he acquired from one series of animals, will 

 apply also to those which most nearly approach them in the analogy of their 

 structure. The gradual increase of the plates or joints of the Crinoidea inclos- 

 ing the abdominal cavity, took place by an extension at their lateral edges, to 

 afford the room required by the viscera in the growth of the animal. The pro- 

 ducing of auxiliary side arms, and reproducing of parts lost, demonstrate the 

 formation of their joints, by a gradual secretion of calcareous matter from the 

 involving muscular covering. These are facts which, since the Comatula; arc 

 so nearly in conformity in their general structure to the Criuoidea, ought also to 

 be demonstrable in their organization. 



The annular basin-shaped plate, which may be considered as the pelvis, 

 appears principally to increase towards its upper margin, as it is on this side 

 only that new auxiliary side arms can be traced as growing out of it, hence its 

 proportions become gradually deeper. This pelvis is (as has been already 

 observed) covered by numerous circular impressions, into which the side arms 

 are inserted ; these circular impressions are surrounded by hexagonal rims, the 

 result of an abundant secretion of calcareous matter from the muscular integu- 

 ment which surrounds and strengthens the adhesion of these side arms at their 

 base. The hexagonal form of these rims appears, as in many other instances, 

 to arise from the mutual pressure and accommodation of the contiguous circles 

 to each other. As this pelvis increases towards its upper edge, new arm joints 

 are there protruded. I have in my possession specimens in which near the 

 upper rim new cavities are formed, having in their centre minute, undeveloped, 

 auxiliary side arms, entirely similar to those of Pentacrinus caput medusae, and 

 where also the claw-like termination has not yet made its appearance. 



The limited number of Comatulae which I have had an opportunity of 

 examining, have not enabled me to ascertain whether the perforation in the ridge 

 which traverses each indentation in the pelvis passes through into the abdominal 

 cavity, or whether the vessel arising from it branches off laterally, and obtains 

 its supplies from vessels under the epidermis which covers the plates 

 externally. 



Each of the five depressiops at the upper rim of the pelvis is of a horse-shoe- 

 like figure, in which the first costal joint rests, to this the second costal joint 

 adheres, and on that a scapula is attached, The TWO COSTALS much resemble 



