312 THE STARFISH LESS. 



epithelium or epidermis (Der. Epthm\ then of a thick 

 fibrous layer (Demi) the derwis or deep layer of the skin, 

 then of a thin and interrupted layer of muscle, and finally, 

 of a layer of coelomic epithelium (Cocl. Epthni] bounding 

 the body cavity. 



The dermis is formed of connective tissue, a substance not 

 met with in Polygordius, formed by the elongation of meso- 

 derm cells into wavy fibres. The ossicles of the skeleton 

 (ps] are formed by deposits of calcium carbonate in the 

 dermis ; the skeleton is therefore a dermal exoskeleton. 

 The large ambulacral ossicles (Ami. os\ however, which 

 bound the ambulacral grooves, lie internal to the vessels 

 (Rad. B. V., Rad. Amb. V.} and have an endoskeletal 

 character. 



The enteric canal passes vertically from mouth (A, MtJi] 

 to anus (An], and is divisible into gullet, stomach (St}, and 

 intestine (hit}. The stomach gives off five wide pouches 

 (Cd. cce], one extending into the base of each arm, and 

 above these five other pouches (PyL cce], each of which 

 divides into two (B, PyL cce) and extends to the extremity 

 of the corresponding arm. The intestine gives off smaller 

 pouches (Int.. cce] which are inter-radial in position. Thus 

 the enteric canal, like the body as a whole, exhibits radial 

 symmetry. The canal is lined by enteric epithelium, mostly 

 endodermal, and is covered externally by ccelomic epithelium 

 (Ccel. Epthm'\ 



Respiration is affected by blind, finger-like offshoots of the 

 ccelome, the respiratory ctzca (Resp. c&\ which pass between 

 the ossicles of the skeleton and project on the surface of the 

 body, thus bringing the ccelomic fluid into close relation 

 with the surrounding water. 



The blood-system consists of a circular vessel (A, C. B. V) 

 round the gullet, connected with a pentagonal vessel round 



