38 INTRODUCTION TO ZOOLOGY chap. 



of very small finger-like processes known as the " marginal 

 lappets." 



The mouth-tube is very short and can only be seen by 

 looking under the bell, but at each corner of the mouth a long 

 "mouth-lobe" hangs down (Fig. 16). These are delicate 

 membranous structures, frilled at the edges and well supplied 

 with stinging thread cells, which render an encounter with a 



Fig. 17. — Aurelia aurita, viewed from below. 



jelly-fish unpleasant to the sea-bather, and from which it 

 acquires the name of the " sea-nettle." If the jelly-fish is viewed 

 from below (Fig. 17), the mouth and mouth-lobes and radial 

 canals are well seen, and also the four brightly-coloured, horse- 

 shoe shaped reproductive organs which contain either the 

 egg cells or the sperms. These are formed from the cells 

 lining the digestive cavity, but they show clearly through the 

 transparent wall. They are at first horseshoe shaped, but 

 each may ultimately form almost a complete ring. Just below 

 each of them is a pit in the under surface of the bell, 

 communicating with the exterior by a small aperture, the 

 sub-genital aperture ; water passes freely in and out of each of 

 these, and this may be of value in renewing the air sujjply, 

 for the water in the pit is only separated from the genital 

 organs by a delicate thin layer of cells. Lying inside the 



