374 



ZOOLOGY 



SECT. 



to this visceral layer of the peritoneum, the wall of the ali- 

 mentary canal and its cseca consists of a muscular layer and an 

 internal lining, the enteric epithelium or endoderm (Ent. Epthm). 

 The coelome is filled with a fluid, the ccelomic fluid, consisting 

 mainly of sea-water, but containing a number of amoeboid cor- 

 puscles (amosbocytes). These collect particles of waste-matters, 

 and when loaded with them pass to the exterior by traversing 

 the walls of the papulse. The latter consist of a muscular 

 layer, an external epidermal layer, and an internal peritoneal layer, 



fee/ 



-EpiAm 



FlQ. 310. Diagrammatic sections of a Starfish. A, vertical section passing on the right 

 through a radius, on the left through an inter-radius. The olf-side of the ambulacra! groove 

 with the tube-feet (T. F.) and ampullae (Amp.) are shown in perspective. B, transverse 

 section through an arm. The ectoderm is coarsely dotted, the nervous system finely dotted, 

 the ectoderm radially striated, the mesoderm evenly shaded, the ossicles of the skeleton 

 black, and the ccelomic epithelium represented by a beaded line. Amb. os. ambulacral 

 ossicles ; Amp. ampullae ; An. anus ; C. Amb. V. circular ambulacral vessel ; C. B. V. 

 septum of ring perihsemal vessel ; Cd. cm. cardiac cseca ; Gael, crelome ; Ccel. Epithm. 

 coelomic epithelium ; Der. Epithm. deric epithelium ; Derm, mesoderm ; Ent. Epthm. 

 enteric epithelium ; Int. cce. intestinal cseca. Mdpr. madreporite ; Mes. mesentery ; Alth. 

 mouth ; Nv. R. nerve-ring ; oc. eye ; os. ossicles of body-wall ; Ovd. oviduct ; Fed. 

 pedicellarise ; p.h. perihsemal spaces ; Pyl. ccec. pyloric caeca ; Had. amb. v. radial ambulacral 

 vessel ; Rad. B. V. points to septum in the radial perihaemal vessel ; Rad. Nv. radial nerve ; 

 Resp. cce. dermal branchiae ; St. stomach ; St. c. stone-canal ; t. tentacle ; T. F. tube-feet. 

 (From Parker's Biology.) 



the internal cavities being in free communication with the 

 ccelome. 



Digestive System. Thp. mouth is found to open through a 

 short passage, the oesophagus, into a wide sac, the cardiac division 

 of the stomach (Fig. 310, St, Figs. 313, 315, card. st). This is a 

 five-lobed sac, each of the lobes of which is opposite one of the five 

 arms. The walls of the sac are greatly folded, and the whole is 

 capable of being everted through the opening of the mouth, by 

 contraction of the muscular fibres of the body-wall, wrapped over 



