no MANUAL OF ZOOLOGY SECT. 



(or. a), situated one at each angle of the mouth and uniting 

 round it. 



At a short distance from each of the straight sides of the 

 mouth is a nearly circular aperture leading into a shallow 

 pouch, the sub -genital pit (s. g. p), which lies immediately 

 beneath one of the conspicuously coloured gonads (gon). 



The mouth leads by a short tube or gullet, contained 

 in the manubrium, into a spacious stomach, which is 

 produced into four wide inter-radial gastric pouches, which 

 extend about halfway from the centre to the circumference. 

 In the outer or peripheral wall of each gastric pouch are 

 three small apertures, leading into as many radial canals 

 (a.r.c, i.r.c, p.r.c), which pass to the edge of the umbrella 

 and then unite in a very narrow circular canal. 



Each gonad (gon.) is a horseshoe-shaped frill-like structure 

 situated on the floor of the gastric pouch. When mature, its 

 products ova or sperms are discharged into the stomach, 

 and pass out by the mouth. The sexes are lodged in distinct 

 individuals. 



Lying parallel with the inner or concave border of each 

 gonad is a row of delicate filaments supplied with stinging- 

 capsules. These are the gastric filaments : their function 

 is to kill or paralyse the prey taken alive into the stomach 

 (compare Fig. 53, g.f). 



The development and life-history of Aurelia present 

 several striking and characteristic features. The impreg- 

 nated egg-cell or oosperm becomes converted into a closed 

 two-layered sac or planula (Fig. 52, A), similar to that of 

 a Hydrozoon. The planula swims about by means of the 

 cilia with which its ectodermal cells are provided, and, after 

 a brief free existence, settles down, loses its cilia, and be- 

 comes attached by one pole. At the opposite pole a mouth 

 is formed. On two opposite sides of the mouth hollow 



