110 



COELEXTERATA. 



n.r 



-c.p. 



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

 (funiiKi lutii-cntrls) from Chun, after O. and R. Hertwig. )' 

 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). 



usually hollow and 

 unbrancbed, more 

 rarely they have a 

 solid endodermal axis 

 (Narcomcdusae, Fig. 

 96, Tesseridac, Ephy- 

 ridae), or are dicho- 

 tomously branched 

 (Cladoncmidae). 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 sj'stem of peripheral canals and pouches 



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

 cavity ; S sub-umbrella ; gonad ; Sh sub-genital pit ; F gastral filament ; S?I muscular 

 system of the sub-umbrella; <// radial canal; Rk marginal body; Rg olfactory pit; Al ocular 

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

 parts of the arms. 



