3466 



COELENTERA TES 



could be got into the mouth if it floated helplessly near, than if it tended at every 

 moment to sink like a stone. The hydra usually multiplies by means of buds which 

 grow out of the body. The offspring often remains attached to the mother until it, 

 in its turn, has given rise to one or two buds. Single eggs, however, develop from 

 time to time in the body wall beneath capsule or wart-like prominences. 



The astonishment of the naturalist Trembley, when he discovered that a hydra 

 cut in pieces was not destroyed, but that the pieces were capable of developing into 

 new individuals, was great. He thought that if the hydras were plants, pieces cut 

 from them would, like young shoots, be capable of further growth. But he had, 

 meantime, come to the conclusion that they were animals, and according to the 

 ideas of the time it was an unheard-of thing that new individuals could grow from 

 cut-off pieces. And thus commenced his experiments of cutting up hydras, which ex- 

 cited the liveliest interest among naturalists in the middle of the eighteenth century. 

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

 parts of the body. Thousands of hydras have been cut 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 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 communica- 

 tion with the digestive cavity of the parent. 



Order SCYPHOMEDUS^ 



In the Scyphomedusae we again have free- 

 swimming jellyfish, stocks developing into jelly- 

 fish, and persistent stocks which never form 

 jellyfish. Whereas in all the Hydromedusae 

 the mouth opens directly into the stomach, in the 

 Scyphomedusae, 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. 3470. Al- 

 though this does not appear important, it indi- 

 Chrysaora (natural size). cates a higher specialization. 



