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 coelome (ccel.) or body-cavity is lined by a 

 ciliated epithelium, the ccelomic epithelium (Ccel. JZpithm.), 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, ampullse, Polian vesicles, etc. 



JrrC.CtC 



Pea 



(Jvd 



TF 



FIG. 280. 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 ampullse (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 

 ctelomic epithelium represented by a beaded line. arnb. os. ambulacral ossicles ; amp. am- 

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

 vessel; '''. (.<-. cardiac cswca ; O< /. coelome ; ('<,/. jiithm. coslomic epithelium; Dei: Ei><tl<n<. 

 deric epithelium ; Derm, mesoderm ; Eiit. Epthm. enteric epithelium ; Int. cce. intestinal caeca 

 Miifn-. iimdreporite ; 3/is. mesentery ; Mth. mouth ; JW. R. nerve ring ; oc. eye ; os. ossicles o:: 

 body wall; ov<l. oviduct; Pal. pedicellariie ; ph. perihsemal spaces; jiiil. cue. pyloric caica 

 Kn'i. i.i, nil. ,-. radial ambulacral vessel; Rail. li. V. points to septum in the radial blood-vessel 

 A'-"'. .Y<-. radial nerve ; RLSP. ne. dermal branchias ; St. stomach ; S1. c. stone-canal ; t. ten- 

 tuck- : 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 coelome is filled with a fluid, the ccelomic fluid, consisting 

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

 puscles (amcelocytes) containing a brown pigment. The dermal 

 branchia3 consist of a muscular' /at/ cr, an external epidermal layer, 

 and an internal peritoneal layer, the internal cavities of the hollow 

 branchi.ie being in free communication with the coelome. 



