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 ccelome is filled with a fluid, the ccelomic fluid, consisting 

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

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

 and when loaded with them pass to the exterior by traversing 

 the walls of the papulae. The latter consist 'of a muscular 

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



cv p ca 



"-7^5gf 



Uertfi 



ZierEpt&m, 



/"SSSK4 Resp.cifJ' 

 I %^= Cfi/k/illim 

 $ ^^^sss^^,^. 



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 ambulacral 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 coelomic epithelium represented by a beaded line. Amb. os. ambulacral 

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

 septum of ring periliEemal vessel ; Cd. cce. cardiac cseca ; Cad. coelome ; Cad. Epithm. 

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

 enteric epithelium ; Int. we. intestinal caeca. Mdpr. madreporite ; Men. mesentery Mtt, 

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

 pedicellanse ; p.h. perihsemal spaces ; Pyl. CMC. pyloric cseca ; Rad. amb. v. radial ainlnilacral 

 vessel ; Rad. B. V. points to septum in the radial perihfemal vessel ; Rail. Nr. radial IRTVI- ; 

 Resp. cce. dermal branchhe ; 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 

 coelome. 



Digestive System. The 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 



