3 o8 THE STARFISH 



ternally of a very thin cuticle, then of a layer of deric 

 epithelium or epidermis (Der. Epthni), 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 ccelomic epithelium (Cxi. Epthm) 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 

 (Os) 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. K, 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 (6V), and 

 intestine (//). The stomach gives off five wide pouches 

 (Cd. Cce), one extending into the base of each arm, and 

 above these five other pouches (Pyl. Cos) 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 

 (Cod. EptH). 



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

 ccelome, the respiratory cceca (Resp. cce.), 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) 



