130 Introduction to Animal Morphology. 



soft, flexible, connective tissue, which calcifies by the deposi- 

 tion of netted, calcareous bands, longitudinally and trans- 

 versely. In Phytocrinus, the stalk at first bends spirally. 

 The body consists of — ist (next the pillar), 2-5 i5(3W plates 

 forming the pelvis. 2nd, one or two circlets of parabasal 

 plates. 3rd, several orders of radial plates along the lines of 

 the arms ; the upper surfaces of these have often two articular 

 faces at an obtuse angle for the two arms {radialia axillaria). 

 There may be also several orders of inter-radial plates. 

 The arms are often branched ; their joints may be free, or 

 united by syzygies (immovable sutures). To these the 

 pinnulse, each of which receives a fine thread from the nerve, 

 are laterally appended. The segments may be numerous ; 

 thus in Pentacrinus briareus there are five basals, fifteen radials, 

 ten primary arms, each of seven joints, two secondary arms of 

 200 joints on each primary, eighteen hundred-jointed pinnae on 

 each secondary arm, and 36,000 ten-jointed pinnules. 



The embryo begins as a free ciliated body, which elon- 

 gates ; a bundle of cilia projects at the anterior end ; then it 

 assumes somewhat the appearance of a four-jointed worm, at 

 each segment of which is a ring of cilia ; a calcareous net- 

 work now forms in the wall, and a mouth develops, which, 

 however, with the cilia is soon lost ; the animal then becomes 

 sessile, somewhat polypoid, develops knobs at its free end 

 and an alimentary canal ; the extended calcareous skeleton 

 masks the growth of the viscera, and the embryo becomes 

 opaque. Within the mouth a set of irregularly lobed gland 

 miasses, brownish in colour, and probably hepatic, appear. 

 The pillar lengthens, and calcifies rapidly. There are about 

 600 fossil, and about 48 known living forms, divided into two 

 families. 



Encrinids — permanently stalked ; calyx either of tables 

 (Tesselata), all fossil forms, ex. Cyathocrinus, Poteriocrinus, 

 &c., or with naked skin between the arms (Articulata). The 

 surviving genera are: — i. Pentacrinus — with small calyx ; ten 

 strong, many-pinnulated arms ; pillar joints five-lobed, with 

 appended cirrhi ; basals, 5; sub-radials, none ; radials, 15 ; 

 inter-radials, none. There are probably four species known. 

 2. Holopus — sessile, aproctous; basals, 4 (5, Ag.) ; radials, 4 



