COELENTERATA. 



103 



into the latter at its lower end. This tube is lined with ectoderm 

 and is called the oesophageal tube, or stomodaeum (Fig. 84 oes). 

 In the second place there projects inwards from the side walls of 

 the body a number of vertical partitions formed of folds of the 

 endoderm and a prolongation of the supporting lamella. These are 

 the mesenteries. Internally they are attached to the oesophageal 



tube in the region of that structure, 



\. \ ' .// while below it they end in free 



edges which are somewhat folded 

 and thickened and are called the 

 mesenterial ridges and filaments. 

 The mesenteries break up the enteric 



.0 



\ 



FIG. 85. Alcyonariau polyp (l r eretittnm 

 cynomorium), from Chun, t pinnate 

 tentacles ; OPS oesophageal tube ; m 

 mesenterial filaments ; s mesenteries ; 

 s', s' two adjacent mesenteries with 

 feebly developed filaments. 



PIG. 86. Diagram of a hexactinian polyp (from 

 Chun, after Andres). / pedal disc ; m wall of 

 body ; p peristome ; d edge of peristome ; 

 t tentacles ; o mouth. 



cavity into a number of circumferential pouches which, in the lower 

 part of the polyp, open into the central part of the enteric cavity 

 or stomach, but in the upper part of the polyp where the mesenteries 

 are attached to the oesophagus form separate chambers (Figs. 88 and 

 89). Each of these communicates above with the cavity of a tentacle 

 (Fig. 84). The gastral pouches then are the peripheral parts of the 

 enteric cavity (coelenteron) between the mesenteries. An opening 

 may be present in each mesentery just below the oral disc putting 



