HYDR^, JELLYFISHES, SEA ANEMONES, CORAL POLYPS 61 



Relation of this branch to the sponges. — The members 

 of this branch resemble the sponges in their fixed mode of 

 living, in their manner of forming colonies by budding, m the 

 possession of one body cavit}', and m certain other ways too 

 intricate to mention here. Hence, it seems that this branch 

 stands nearer the sponges than any other branch of the 

 Metazoa, but is higher in the scale than the sponges. For 

 instance, we find the beginnings of a nervous system. In 

 some of the jellyfish the nervous system consists of two 

 rings of nerve matter around the edge of the umbrella. 

 This is the first example of a concentrated, well-defined 

 nervous system. The nervous system in the sea anemones 

 consists of nerve cells and fibers irregularl}^ disposed 

 throughout the body. The methods of reproduction are 

 more specialized than in the sponges, as are also the mode 

 of living and the life history. 



Adaptations to mode of living and environment. — An 

 animal, to live, must have food. This food must either be 

 brought to the animal, or the animal nmst go to it. Many 

 of the animals in the foregoing branch are fixed ami cannot 

 go to their food. Such members have long, slender ten- 

 tacles with which they can catch the food as it passes by 

 and convey it to the mouth, — notably the fresh-water 

 hydra. The hydractinia, a complex coelenterate, is even 

 better adapted than this. It attaches itself to the shell of 

 the hermit cral), and is thus carried to new fields of food. 

 At the same time it falls heir to minute morsels of the 

 crab's food. It ]-iays for all this, however, by affording 

 |_irotection to the crali, of which we shall speak latei-. 



It will be remembered that nearly all of the Coelenterata 

 are soft-bodied animals. In the ocean they are alwavs 

 ^•urrounded by hordes of enemies, who would quickly 



