THE JELLY-FISH 1329 



edge that the hydra was the child of the jelly-fish 

 was obtained many years ago by a Scotch and by a 

 Scandinavian naturalist. It was known that some 

 small kinds of jelly-fish which were kept in sea-water 

 in an aquarium disappeared altogether in the late 

 autumn. Then it was noticed that there were many 

 very small things with tentacles, on the sides of the 

 glass, which had not been noticed before. And at 

 last the curious discovery was made that these hydras 

 or planulas reproduced jelly-fish the next year. This 

 is a very strange story, and the course of nature's 

 proceeding is, that when food has become scarce and 

 the boisterous waves would become fatal to the deli- 

 cate Medusa, it shall lay eggs which produce crea- 

 tures that can settle down out of the way of the rush 

 of water, and that require but little food. Then in 

 the next year when food is in plenty, the progeny 

 separate into jelly-fish like the parent. The hydras 

 or progeny have no power of laying eggs; they digest 

 and produce the creature that shall lay eggs. The 

 Scandinavian naturalists and Germans called this 

 "alternate generation," and named the hydra the 

 nurse of the jelly-fishes. This is the method by 

 which most of the jelly-fish, which may be occasion- 

 ally seen stranded on the coast, were produced; 

 but there are some whose planulas do not settle 

 down, but are always free swimmers, and they divide 

 into Medusae in the sea. 



This intensely interesting course of life is modified 

 in all the hundreds of kinds of creatures which are 

 connected with the jelly-fish in classification, by their 

 having many structures in common. The creatures 



