312 THE STARFISH LESS. 



epithelium or epidermis (Der. EptJwi], then of a thick 

 fibrous layer (Derm) the dermis or deep layer of the skin, 

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

 of a layer of coelomic epithelium (CoeL Epthui] 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 

 (as) are formed by deposits of calcium carbonate in the 

 dermis ; the skeleton is therefore a dermal exoskeleton. 

 The large ambulacral ossicles (Amb. 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, Mth) 

 to anus (An), and is divisible into gullet, stomach (St\ and 

 intestine (Int). 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 coelomic epithelium 

 (Ccel. Epthm'}. 



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

 coelome, the respiratory cczca (Resp. coe], which pass between 

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

 body, thus bringing the coelomic 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 



