492 



CCELENTERA TES. 



of cutting up hydras, which excited the liveliest interest among naturalists 

 in the middle of last century. 



The hydra is also remarkable on account of its capacity for regenerating 

 lost parts of the body. Thousands of hydras have been cat up in all possible 

 ways, grotesque monsters being produced of which drawings were made. Trembley 

 also made attempts to turn the hydra inside out, like the finger of a glove. 

 His first experiments of this sort with fasting animals were not successful, but 

 he succeeded with others which had been well-fed. Animals thus treated often 

 succeeded in returning to their natural condition. 



The formation of buds was w^atched with care by Rosel, who did not fail to 

 notice that the digestive cavity of the young polyps, growing out at various parts 

 of the parent animal, even when provided with functional mouths and arms of their 

 own, still remained in open communication with the digestive cavity of the parent. 



Order SCYPHOMEDUS^E. 



In the Scyphomedusae we again have free-swimming jelly-fish, stocks developing 



into jelly-fish, and persistent stocks which never 

 form jelly-fish. Whereas in all the Hydromedusaa 

 the mouth opens directly into the stomach, in the 

 Scyphomedusse, and their attached and related 

 forms, the skin round the mouth has been drawn in 

 to form a tube which opens some way down into 

 the stomach; the dra wing-in of this mouth-tube, or 

 oesophagus, having led to the formation of ridges 

 on the wall of the stomach, which hold the inner end 

 of the tube in place, as shown in the illustration of 

 Monoxenia, on p. 496. Although this does not ap- 

 pear important, it indicates a higher specialisation. 

 Taking first the free-swimming jelly-fish, the 

 larger and more characteristic forms are distin- 

 guished by their delicate colouring. The yellow 

 and yellowish red Chrysaora ocellata are seen 

 floating past in thousands off the southern coast 

 of Norway. The western harbours of the Baltic 

 Sea, after continuous northerly winds, are often 

 filled with whole banks of the blue Aurelia 

 aurita, and the splendid Rhizostoma are con- 

 stantly to be met with in the Mediterranean and 

 Adriatic Seas. On a fine spring day they are 

 almost always to be found on the shore, where 

 these large, reddish blue, living hemispheres are 

 wrecked, and soon melt away. Indeed, the 

 bodies of all jelly-fish contain so large a pro- 

 portion of water that when a tolerably large specimen is laid on blotting-paper it 

 evaporates, leaving no other trace than its outline on the paper. In these 



Chrysaora (nat. size). 



