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CHAPTER XIV. 



ORDER IV. CRINOIDEA. 



THE Crinoids or Sea-lilies are Echinodermata, in which the 

 body is fixed, during the whole or a portion of the existence of 

 the animal, to the sea-bottom by means of a longer or shorter, 

 jointed, and flexible stalk. The body is distinct, composed of 

 articulated calcareous plates, bursiform, or cup-shaped, and 

 provided with branched arms, which are typically from five 

 to ten in number, are independent of the visceral cavity, 

 and are grooved on their upper surfaces. (The position 

 of the body being reversed, the upper surface is ventral ; 

 whilst the dorsal surface is inferior, and gives origin to 

 the pedicle.) The tubular processes, however, which are 

 given off from the radiating ambulacral canals of the Crin- 

 oidea, unlike those of the Echinoidea and Asteroidea, are not 

 used in locomotion, but have probably a respiratory function. 

 The mouth is central, and looks upwards, an anal aperture 

 being sometimes present, sometimes absent. The ovaries are 

 situated beneath the skin in the grooves on the ventral sur- 

 faces of the arms or pinnules, as are also the ambulacral or 

 respiratory tubes. The arms are furnished with numerous 

 lateral branches or " pinnulse." The embryo is " free and 

 ciliated, and develops within itself a second larval form, 

 which becomes fixed by a peduncle " (Huxley). 



If we take such a living Crinoid as Rhizocrinus (fig. 150), 

 we shall be able to arrive at a comprehension of the leading 

 characters of this order. Rhizocrinus is one of those Crinoids 



