ANNULOIDA: ECHINODERMATA. 175 



permanently fixed, but is only attached by a stalk when young 

 (fig. 64, /;), in which condition it was described as a distinct 

 species under the name of Pentacrinus Europeans. In its adult 

 condition, however, the Comatula is free, and consists of a pen- 

 tagonal disc, which gives origin to ten slender arms, which are 

 fringed with many marginal pinnulae or " cirri." The mouth 

 and anus are on the ventral surface of the disc, which in this 

 case is again the inferior surface, since the animal creeps 

 about by means of its pinnated arms. The arms, in fact, of 

 Comatula appear to be purely locomotive in function, and to be 

 never employed as prehensile organs. The animal lives upon 

 very minute organisms, drawn into the mouth by the action of 

 the cilia lining the alimentary canal. The dorsal cirri, however, 

 are employed to moor the animal temporarily to solid objects. 

 The mouth is central in position, and the anus, which in some 

 species forms a tubular projection, is situated on one side. 

 Both the arms and the lateral pinnulae are grooved on their 

 ventral surfaces for the ambulacral vessels ; and the pinnules 

 also serve for the support of the reproductive organs. It is 

 extremely doubtful if the ambulacral system, in the adult, has 

 any communication with the exterior. The function, in fact, 

 of the water-vascular system appears to be wholly respiratory, 

 locomotion being entirely effected by means of the arms. The 

 alimentary canal is confined entirely to the disc, and the 

 stomach sends no diverticula along the arms as it does in the 

 Aster oidea. The larva or pseudembryo of Comatula rosacea is 

 a small ovate organism, with four transverse ciliated bands, a 

 key-hole-shaped mouth, and a small vent and rudimentary in- 

 testine, the whole showing no traces of radiation. The young 

 Crinoid is produced within the pseudembryo, and develops a 

 fresh mouth, anus, and stomach for itself; the first being 

 originally oro-anal in function, and being placed in the centre 

 of the ambulacral system. 



Several species of Comatula are known, and the genus 

 appears to be cosmopolitan in its distribution. The genus 

 Ophicrinus has been formed for species said to possess no 

 more than five undivided arms. 



ORDER CYSTOIDEA ( Cystidea). The members of this order are 

 all extinct,* and are entirely confined to the Palaeozoic period. 

 The body (fig. 65) was more or less spherical, and was pro- 

 tected by an external skeleton, composed of numerous poly- 



* Recently Professor Loven has described a singular Australian Echino- 

 derm as being most closely allied to, if not truly referable to, the order 

 Cystoidea. He has named this curious form Hyponome Sarsi, and believes 

 it to be nearly related to the Cystidean genus Agelacrinites. 



