THE EVOLUTION OF MAN 



life, there lived creatures of a simple structure, 

 such as that of the present-day Gastrula-larvae, 

 or that of Pemmatodiscus, which are swimming 

 about freely and represent creatures that persist 

 all their lives in this stage. We may agree with 

 Haeckel in thinking that these most ancient skin- 

 and-stomach animals, for which Haeckel has pro- 

 posed the general term of "Gastraea," at a very 

 early stage tried two avenues of development. 

 Some attached themselves with the closed end of 

 their cylinders to the bottom of the sea and thus 

 developed into a Hydra form. In the further de- 

 velopment of this type followed a swarm of other 

 sea animals, the so-called plant and flower types, 

 such as sponges, corals, etc. But another group 

 of the Gastrula forms adopted the creeping mode 

 of life. Their bodies gradually approached the 

 form of a symmetrical cylinder. This would be 

 the line leading to genuine worms and then 

 through vertebrates to man. At any rate we have 

 for the present no simpler logical conception of 

 the road which we traveled, and logic is indis- 

 pensable so long as we are dealing with circum- 

 stantial evidence. 



And now only one more short chain of conclu- 

 sions remains the last glowing mountain top in 

 the morning light of our line of vision, before 

 the curtain of white mist is drawn across it. 

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