306 SEA-ANEMONES, ZOOPHYTES, ETC. 



although Cydippe has been kept alive a little time, 

 and we have seen the larval Medusa at Brighton and 

 the Crystal Palace, not bigger than a pin's head, 

 which had been hatched in the tanks. The pretty 

 little Hydra-tuba may also be searched for and found 



Fig. 237. 



Hydra-tuba, in various stages of segmentation. 



in these places ; and in them, again, we have evi- 

 dence of how "jelly fishes" can be formed from an 

 object less than half an inch in height, by the "seg- 

 mentation," or splitting up into free parts, of saucer- 

 like objects, which turn over into umbrella-like disks, 

 and then swim away, as utterly unlike their parents 

 as any two animals can well be. 



Sponges will always be difficult objects to keep 

 alive under artificial conditions, although we have 

 seen that the most delicate of all of them, the fresh- 

 water sponge (Spongilla fluviatilis) has succumbed to 

 the will and care of man in this respect. Several of 

 our commonest British sponges are kept alive at 

 Brighton, Manchester, and especially at Sydenham, 



