110 



COELENTERATA. 



usually hollow and 

 unbranched, more 

 rarely they have a 

 solid endodermal axis 

 (Narcomedusae, Fig. 

 96, Tesseridae, Ephy- 

 ridae), or are dicho- 

 tomously branched 

 (Cladonemidae). Be- 

 sides the larger main 

 tentacles there are 

 often smaller inter- 

 mediate tentacles at 

 the umbrella edge 

 (Tessera, Fig. 133). 

 Occasionally the ac- 

 cessory tentacles are 

 confined to the young 

 stages and drop off 

 in later life, or they 

 may become trans- 

 formed into the mar- 

 ginal bodies. 



In the gastrovascular apparatus a central stomach for digestion, 

 and a carrying or circulating system of peripheral canals and pouches 



tb. 



FIG. 96. Portion of the edge of the umbrella of a Narcomedusan 

 (Cunina lativentris) from Chun, after O. and K. Hertwig. v 

 velum ; t tentacles with stiff endodermal axes ; t.b roots of 

 tentacles ; n.r nerve ring ; n.s radial nerve which passes to the 

 base "of the tentacles ; ot marginal bodies ; x otoporpa ; g.t 

 gastral pouches ; c.p, c.p the two peronial vessels ; they form 

 originally a part of the circular canal, which in the shifting 

 of the tentacles dorsalwards on to the ex-umbrella is festooned 

 and opens into the gastral pouches (after Hertwig, from Chun). 



Z 



FIG. 97. Diagrammatic longitudinal section through a Rhizostoma. U umbrella ; M gastric 

 cavity ; S sub-umbrella ; G gonad ; Sh sub-genital pit ; F gastral filament ; SM muscular 

 system of the sub-umbrella; ligf radial canal; Blc marginal body; Eg olfactory pit; Al ocular 

 lobe ; Sk shoulder tufts, Dk dorsal tufts, Vk ventral tufts of the eight arms ; Z terminal 

 parts of the arms. 



