352 



ZOOLOGY 



SECT. 



titions, developed in the outer of these two layers. Each ossicle 

 consists of a close network of calcareous rods. Between contiguous 

 ossicles extend bands of muscular fibres. 



The interior of the ccelome (ccel.) or body-cavity is lined by a 

 ciliated epithelium, the ccelomic epithelium (Cod. Epithm.\ which 

 not only covers the inner surface of the body-wall as the parietal 

 layer, but forms an investment also for the contained organs 

 the various parts of the alimentary canal and its appendages, the 

 genital glands, the madreporic canal, ampullae, Polian vesicles, etc. 



Mdj. 



Ovd 



FIG. 280. J)iagrammatic 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.) are 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. amb. os. ambulacral ossicles ; amp. am- 

 pullae ; an. anus ; C. Amb. V. circular ambulacral vessel ; C. B. V. septum of ring blood- 

 vessel ; Cd. cce. cardiac cseca ; Gael, ccelome ; Cad. JSpithm. ccelomic epithelium ; Der. Epitlnn. 

 deric epithelium ; Derm, mesoderm ; Ent. Epthm. enteric epithelium ; Int. cai. intestinal cseca ; 

 M<1 i>r. madreporite ; Mes. mesentery ; Mth. mouth ; JVr. R. nerve ring ; oc. eye ; os. ossicles of 

 body wall ; ord. oviduct ; Ped. pedicellarise ; ph. perihsemal spaces ; pyl. cctc. pyloric caeca ; 

 A'"-/. n,,>/>. <. radial ambulacral vessel ; Rod. B. V. points to septum in the radial blood-vessel ; 

 lia<l. Nr. radial nerve ; Resp. cce. dermal branchiae ; St. stomach ; St. c. stone-canal ; t. ten- 

 tacle ; T. F. tube-feet. (From Parker's Biology.) 



In addition to this visceral layer of the peritoneum, the wall of 

 the alimentary canal and its caeca consists of a muscular layer and 

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

 The ccelome is filled with a fluid, the co&lomic fluid, consisting 

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

 puscles (amcebocytes) containing a brown pigment. The dermal 

 branchiae consist of a musmlo^ '^ ^ an external epidermal layer, 

 and an internal portion^ m ^ e ^''^al cavities of the hollow 

 branchi* being in fre th the ccelome. 



