106 



COELENTERATA. 



form of a diffuse plexus of much-branched glanglion cells, which are 

 contained in both ectoderm and endoderm between the lower ends of 

 the epithelial cells, and are especially developed in the peristome, 



tentacles, and oesophagus. 



The AntJiozoa are almost 

 always dioecious, rarely her- 

 maphrodite ( Cerianthus) . va 

 and spermatozoa arise from 

 the endoderm al cells of the 

 mesenteries, and lie in follicles 

 in the jelly of the same struc- 

 tures. They cause swellings on 

 the faces of the mesenteries, 

 a short distance from their 

 free ends (Fig. 91). Asexual 

 reproduction by budding and 

 fission is very generally present, 

 and often leads to the forma- 

 tion of colonies. The Antho- 

 zoan polyps are much inclined 

 to the formation of skeletal 

 structures, which consist of 

 slimy (Cerianthus), horny, or 

 calcareous substances. 



The symmetry of the Antho- 



zoan polyps is almost always radial. The Octactinia (Alcyonarid) 

 indicate their 8-radiate structure by their eight feathered tentacles, 



m.p. 



FIG. 90. Primary mesentery of a Hexactinian 

 (Sagartia parasitica), and the parts of the body 

 to which it is attached, ac Acontia ; c Septal 

 ostium ; / pedal disc ; m.l longitudinal mus- 

 cular fibres; m.t transverse muscular fibres; 

 m.p parietal muscles ; p peristome, t tentacle. 



FIG. 91. Section through the mesentery of an Actinian (Edwardsia tulcrculata), after O. and 

 R. Hertwig. ck ectoderm ; en endoderm ; m./mesenterial filament; m.l section of the pro- 

 jection caused by the folding of the muscular lamella of the longitudinal muscles, the fibres 

 appear as dots ; ov ovary. 



