HTDBOZOA SCTPHOMEDUS.E. 



253 



The form of the gastrovascular apparatus exhibits considerable 

 differences, which in the Dlscophora may be considered as modifica- 

 tions of the E'fhyra type. The flat disc of the Epliyra, which 

 is split into eight pairs of lobes, contains a central gastric cavity 

 into which the canal of the short, wide, four-cornered manu- 

 briuin leads. From this central cavity there diverge eight canal- 

 like peripheral diverticula (radial pouches), between which there are 

 formed sooner or later in the vascular lamella the same number of 

 short intermediate canals (intermediate pouches). The radial and 

 intermediate ca.nals sometimes become enlarged, as in Pelagia and 



Z 



FIG. 196. Section through the olfactory pit, the sen?e-organ (marginal body) and its nerve 

 centre, of Aurelia aurita. K, Olfactory pit ; L, lobe of the umbrella covering the 

 sense organ ; P, eye spot ; Of, otolith of the auditory sac ; Z, cells after solution of the 

 otoliths ; En, entoderm ; EC, ectoderm with the underlying layer of nerve fibrilla;, F. 



Chrysaora, so as to form unusually broad gastric pouches separated 

 by thin septa and without any communication with each other at 

 the periphery. Sometimes, however, they become transformed into 

 narrow vessels, between which, in the broad intervening septa, there 

 is secondarily developed during the subsequent growth by a separa- 

 tion of the two layers of the vascular-lamella, a rich network of 

 anastomosing canals, and near the edge of the disc a circular canal 

 (Aurelia, Rhizostomci). 



