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 watched with care by Rdsel, 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 Hydromedusae 
the mouth opens directly into the stomach, in the 
Scyphomedusas, 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 drawing-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 
