ANNULOIDA: ECHINODERMATA. !$! 



about by means of its pinnated arms. The mouth is central 

 in position, and the anus, which in some species forms a tubu- 

 lar projection, is situated on one side. Both the arms and the 



Fig. 43. Crinoidea. Comatula rosacea, the Feather-star; a Free adult; 

 b Fixed young. (After Forbes.) 



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 en- 

 tirely 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 Asteroidea. 



ORDER CYSTOIDEA (Cystidea). The members of this order 

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

 period. The body (fig. 44) was more or less spherical, and 

 was protected by an external skeleton, composed of numerous 



* 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 Sarst, and believes 

 it to be nearly related to the Cystidean genus Agelacrinites. 



