170 



SYSTEMATIC ZOOLOGY. 



tions of the mesenterial filaments can be more readily 

 absorbed. Further details of structure are better given 



FIG. 17. Model of a Scyphozoan, part of the wall cut away to show the internal 

 structures. At the top is the oral disc with three tentacles. The o?sophagus 

 extends, in the centre, into the digestive cavity, the cavity being subdivided 

 by radial septa. In the cut edges of the walls and septa the ectoderm is left 

 white, the entoderm is divided into blocks. 



in treating of the two subclasses into which the Scyphozoa 

 are divided, merely saying here that all are marine. 



