208 MANUAL OF ZOOLOGY. 



of the existence of the animal, to the sea-bottom by means of a 

 longer or shorter, jointed, and flexible stalk. The body is dis- 

 tinct, composed of articulated calcareous plates, bursiform, or 

 cup-shaped, and provided with slender arms, which are typi- 

 cally five or ten in number, and are grooved on their upper 

 surfaces for the ambulacra. (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 Crinoidea, unlike those of the Echi- 

 noidea 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 surface of the arms or 

 pinnules, as are also the ambulacral or respiratory tubes. The 

 arms are furnished with numerous lateral branches or "pin- 

 nulse." The embryo is "free and ciliated, and develops within 

 itself a second larval form, which becomes fixed by a ped- 

 uncle" (Huxley). 



If we take such a living Crinoid as Rhizocrinus (fig. 101), 

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

 characters of this order. Rhizocrinus is one of those Crinoids 

 which is permanently rooted to some foreign object by the 

 base of a stalk which is composed of a number of calcareous 

 pieces or articulations. In some cases (as in Apiocrinus) the 

 base of the stem or "column" is considerably expanded.- In 

 other cases the column is simply " rooted by a whorl of ter- 

 minal cirri in soft mud" (Wyville Thomson). The joints of 

 the column are movably articulated to one another, the joint- 

 surfaces often having a very elaborate structure, so that the 

 entire stem possesses in the living state a greater or lesser 

 amount of flexibility. Each joint is perforated centrally by a 

 canal, which by the old writers was very inappropriately termed 

 the " alimentary canal," but which in truth has nothing to do 

 with the digestive system of the animal. At the summit of the 

 stem is placed the body, which is termed the " calyx," and which 

 is usually more or less cup- shaped, pyriform, bursiform, or dis- 

 coidal. The calyx exhibits two surfaces, a dorsal and a ventral, 

 of which the dorsal is composed, wholly or in part, of calcareous 

 plates articulated by their margins, whilst the former is com- 

 posed of a more or less leathery integument, strengthened by 

 the deposition in it of numerous small plates of carbonate of 

 lime. The ventral surface exhibits the aperture of the mouth, 

 which may be subcentral or may be very excentric, and which 



