Ovd. 



FIG. 76. Diagrammatic sections of a Starfish. 



A, vertical section passing on the right through a radius, on the left 

 through an inter-radius. The off-side of the ambulacral groove, with 

 the tube feet ( T. F) and ampullae (Amp), is shown in perspective. 



B, transverse section through an arm. 



The ectoderm is coarsely dotted, the nervous system finely dotted, the 

 endoderm radially striated, the mesoderm evenly shaded, the ossicles of 

 the skeleton black, and the ccelomic epithelium represented by a beaded 

 line. 



The body-wall consists of deric epithelium (Der. Epthm), dermis 

 (Derm), and the parietal layer of ccelomic epithelium (Cat. Epthm). 



To the body-wall are attached pedicellarias (Ped), and the end of the 

 arm bears a tentacle (/) with an ocellus (oc) at its base. 



The skeleton consists of ossicles (os) imbedded in the dermis : large 

 ambulacral ossicles (Amb. os) bound the ambulacral grooves on the 

 ventral surfaces of the arms. 



The mouth (Mth} leads by a short gullet into a stomach (St), which 

 gives off a cardiac caecum (Cd. c<z) and a pair of pyloric caeca (Pyl. C<K) 

 to each arm, and passes into an intestine (Int) which gives off intestinal 

 caeca (Int. cce) to the inter-radii, and ends in the anus (An). The 

 pyloric caeca are connected to the dorsal body- wall by mesenteries 

 ( Mes. in B). The wall of the enteric canal consists of enteric epithelium 

 covered by the visceral layer of ccelomic epithelium ( Gael. Epthm'}. 



From the ccelome are given off respiratory caeca (Resp. eft), which 

 project through the body- wall : the latter contains spaces (p. /i) derived 

 from the coeloiue. 



