188 



ZOOLOGY 



are produced into slender threads — the aconlia — which may be 

 protruded through the mouth or through special apertures 

 (cinolidcs) of the body -wall (Fig. 138, A.) 



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

 the two preceding classes. The body-wall (Fig 138)— base, column, 

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

 within, and between them an intermediate layer or mesogloea, 

 which is extremely thick and tough. The gullet {r/uL), 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-mescnteric chambers — is endodermal. The mesenteries(«(fs.) 

 consist of a supporting plate of mesogloea, co-vered on both sides by 



'■nl. Tnes. C 



Fia. 138 — Diagi'aTnmatic vertical (A) and transverse (B) sections of a Seav-anemone. The 

 ectoderm is dotted, the endoderm striated, tlie mcsogloeai black, ar. acontium ; en. cinclis ; 

 gid. gullet ; int. nies. c. iuter-mesenteric chamber ; mcs, mesentery ; vies. /. mesenteric 

 filament ; mth. mouth ; ost. ostium ; x*. 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 



