260 



NATURE STUDY IN SCHOOLS. 



Second, the digestive and circulatory system which is adapted to meet 

 the wants of the individual. 



Third, the nervous system, which not only guides the other organisms 

 in their labors, but is of a sufficiently high order to cause the various cellu- 

 lar tissues to band together to repair damages which are detrimental to the 

 individual. 



Fig. 127. 



Spiculijenous Sponges. 



PROVINCE COELiEtfTREATA. 



Hydras, Hydroids, Sea Anemonies, Corals, etc. 



In the type of this class of animals we find that the 

 cells have become even more differentiated than in the 

 sponges, producing true tissues and not simply a kind of 

 rudimentary flesh. There is a body which contains a fixed 

 mouth that opens into a sac, suspended within the cavity of 

 the body, the stomach. The mouth serves for the purpose 

 of taking the food, while the undigested portions are thrown 

 out of it. See fig. 128 with explanation of parts beneath 

 the cut. Between the stomach sac and the walls of the 

 body are often chambers which serve as digestive, circula- 

 tory and reproductive cavities. See fig. 128. The mouth 

 is surrounded by tentacles, the function of which is to 

 gather food, serve as respriatory organs, and in some cases 

 as organs of locomotion. 



