ANNULOIDA: ECHINODEKMATA. 133 



CHAPTER XXI. 

 CRINOIDEA, CYSTOIDEA AND BLASTOIDEA. 



ORDER CRINOIDEA. The members of this order are Eclii- 

 nodermata, 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 solid arms, which are 

 primarily from five to ten in number, are independent of 

 the visceral cavity, 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 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 surfaces of the arms or pinnules. 

 The arms are furnished with numerous lateral branches or 

 * pinnulee.' The embryo is ' free and ciliated, and develops 

 within itself a second larval form, which becomes fixed by a 

 peduncle.' (Huxley.) 



Of those Crinoidea which are permanently fixed to the sea- 

 bottom by a jointed pedicle, there exist but one or two living 

 forms, of which the best known is the Pentacrinus Caput- 

 Medusce. In this type of the Crinoidea largely represented 

 in past geological epochs the body is composed of a series of 

 calcareous plates, united together so as to form a cup, or 

 1 calyx,' the bottom of which is continued into a ' column,' or 

 pedicle, composed of a series of calcareous joints or articula- 

 tions, whereby the animal is fixed to some foreign body. The 

 upper part of the calyx is roofed over by a series of calcareous 

 plates, and is perforated by the apertures of the mouth and 

 anus, the latter being sometimes absent. In the recent 

 species the mouth is central, and there is a distinct anus 

 at one side. The margin of the calyx gives origin to the 

 arms, which are grooved on their upper (or ventral) sur- 

 faces for the ambulacra. In the living Crinoids the am- 

 bulacral grooves are continued along the upper surface of the 

 calyx to the mouth. In the Palaeozoic Crinoids there is only 

 a single opening on the upper surface of the calyx, which is 

 sometimes central and sometimes lateral, and which serves 

 both as a mouth and anus. In many cases this aperture is 

 level with the surface of the calyx, but in many species it is 



