

PHYLUM CCELENTERATA 



159 



appear through the transparent umbrella as coloured horseshoe- 

 shaped patches. Their precise position is seen by cutting away a 

 portion of the ex-umbrella so as to expose one of the gastric 

 pouches from above (Fig. 113, A). It is then seen that the 

 gonad (gori) is a frill-like structure lying on the floor of the 

 pouch and bent in the form of a horse-shoe with its concavity 

 looking inwards, i.e. towards the mouth. Being developed from 



FIG. 114. Aurelia aurita. A, side view, one-fotr.th of the umbrella cut away ; B. diagrammatic 

 vertical section, ectoderm dotted, endoderm striated, mesogloea black ; circ. c. circular canal ; 

 g.f. gastric filaments ; gon. gonad ; g. p. gastric pouch ; gal. gullet ; h. hood ; i.r. c. inter-radial 

 canal; mg. Ip. marginal lappet ; mth. mouth; or. a. oral arm; s.g. p. sub-genital pit; st. 

 stomach. 



I 



the floor of the enteric cavity, the gonad is obviously an 

 ondodermal structure: when mature, its products ova or sperms 

 ^are discharged into the stomach and pass out by the mouth. 

 Here, then, is an important difference from the Hydrozoa^ in 

 which the generative products are usually ectodermal, and are 

 always discharged directly on the exterior. The sexes are lodged 

 in distinct individuals. 



