LIFE, ITS PHYSICAL B.4SIS A.NU SlMl-Ll^sL L.M-,;,..ssi..,.N .-(7 



/ 



Fig. 27. — Diagi-am showing fundamental structure of types of several nniinnt ptiyiA: 

 1, sea anemone; 2, starfish; 3, worm; 4. centipe.le; 5. clam; 0. honeylnf; 7. 

 mander. In ei ch figure the central nervous system is indicated I'y the Mack Im. - 

 (After Haeckel.) 



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But great periods of tliis time (ire shut iiway fioni i;.s wiiliout 

 record of their duration, and lon<^ series of the i^radu.-dly 

 changing forms are lost to us withor.t I.ojU' of discovery. And 

 yet in its large outlines we know the liistory of all this time 

 and the character of all these gratletl series. 



