392 



ZOOLOGY 



SECT. 



Fia. 314. Metacrinus interruptus. 



(After P. H. Carpenter.) 



in the larva, and the 

 place of its terminal ossicle 

 is taken by a plate the 

 eentro-dorsal ossicle of the 

 disc. To the eentro-dorsal 

 ossicle are attached whorls 

 of many-jointed, slender, 

 curved dorsal cirri. 



The mouth in all the 

 Crinoidea, with one ex- 

 ception (Actinometra), is 

 situated in the centre of 

 the ventral (upper) sur- 

 face, and the anus in all, 

 with the same exception, 

 is excentric and inter- 

 radial. Running outwards 

 from the mouth are a 

 series of very narrow am- 

 lulacral grooves, one of 

 which runs outwards on 

 the ventral surface of each 

 arm, giving off branches 

 to the arm-branches and 

 to the pinnules. Bordering 

 the ambulacral grooves 

 and their branches are a 

 pair of rows of short 

 tubular tentacles, which 

 correspond morphologi- 

 cally with the tube-feet 

 of the other classes, but 

 are devoid of the terminal 

 suckers, and are not loco- 

 motor, but probably sen- 

 sory and respiratory in 

 function. 



The coelome in the 

 Echinoderms is a wide 

 cavity lined by a ciliated 

 coelomic epithelium and 

 containing a corpusculated 

 fluid. Prolongations of it 

 pass out into the rays, 

 and, in the Ophiuroidea 

 and Asteroidea, between 

 the layers of the body- 

 wall. In the Crinoidea 



