THE CCELENTERATES 



135 



signifies 'nettles,' and they are popularly known as sea nettles. 

 They all possess stinging cells, which are distributed most thickly 

 in the tentacles, and some of the larger species are undoubtedly 

 able to produce an impression on the bodies of unwary bathers, 

 while almost all have the power of paralysing the living prey on 

 which they feed. 



By far the. commonest of the jelly-fishes of our seas is the 

 beautiful blue medusa Aurelia aurita. This species appears in 

 enormous shoals during the 

 summer, and large numbers 

 are washed upon flat, sandy 

 beaches. They vary in size 

 from two or three inches 

 to nearly a foot in dia- 

 meter, and may be recog- 

 nised from our illustration. 

 The ' bell ' is umbrella- 

 shaped, and is so trans- 

 parent that the stomach 

 with its radiating canals 

 may be seen through its 

 substance. Around the mar- 

 gin there are little pigment 

 spots which are supposed 

 to be rudimentary eyes, and 

 Little cavities, containing a 

 clear fluid, that are thought 

 to serve the purpose of ears. 



On the under surface 

 may be seen the square 



mouth, furnished with four FlG< 85. Aurelia aurita 



long and graceful frilled 



lips, which are richly supplied with stinging cells; also the lour 

 ovaries or egg-producing organs, rendered conspicuous by their 

 violet colouring. 



The life history of Aurelia is most interesting. The eggs are 

 produced in pouches that communicate directly with the stomach- 

 cavity, and these give rise to little ciliated larvae that are ejected 

 through the mouth, and then swim about freely in the water for 

 a time. After this they settle at the bottom, lose their cilia, and 

 become little cylindrical jelly-fishes, fixed by a short stalk-like foot 



