PHYLUM CCELENTERATA 



175 



below the gullet is produced into a curious twisted cord, the 

 mescntcric filament (mes. /.), answering to the gastric filaments of 

 the Scyphozoa. 



The general arrangement of the cell-layers is the same as in 

 the two preceding classes. The body-wall (Fig. 125) base, column, 

 and disc consists of a layer of ectoderm outside, one of endoderm 

 within, and between them an intermediate layer or mesoglcea, 

 which is extremely thick and tough. The gullet (<jul.\ which, like 

 that of the Scyphula, is an in-turned portion of the body-wall, is 

 lined with ectoderm, and its outer surface i.e. that facing the 

 inter-mesenteric chambers is endodermal. The mesenteries (mes.) 

 consist of a supporting plate of mesoglcea, covered on both sides by 



B 



FIG. 125. Diagrammatic vertical (A) and transverse (B) sections of a Sea.-anemone. The 

 ectoderm is dotted, the endoderm striated, the mesoglo3a> black, ac. acontium ; en. cinclis ; 

 1 1 vl. gullet; int. mes. c. inter-mesenteric chamber; mes. mesentery; mes. f. meseiiteric 

 filament ; mth. mouth ; ost. ostium ; p. pore ; t . tentacle. 



endoderm. The tentacles (t) are hollow out-pushings of the disc, 

 and contain the same layers. 



Muscular System. Sea-anemones perform various charac- 

 teristic movements : the column may be extended or retracted, the 

 tentacles extended to a considerable length, or drawn back and 

 completely hidden by the upper end of the column being folded 

 over them like the mouth of a bag; the gullet, and even the 

 mesenteries, may be partially everted through the mouth ; and 

 lastly, the whole animal is able, very slowly, to change its position 

 by creeping movements of its base. 



These movements are performed by means of a very well- 

 developed set of muscles. A mesentery examined from the surface 



