A Three-fold Development. 147 



In the second line of development was animal life 

 also, and that would have begun after plant life, but with 

 a much shorter interval than that which passed before 

 the first plants existed. A little more cooling down be- 

 low the temperature in which plants could live, and the 

 first animal life must have appeared. Their food was 

 ready for them, and when other conditions were suitable 

 the first beings which could have been called animals 

 came into existence. The change from plant to animal is 

 not wide, as some plants in their immature stage behave 

 like animals, darting through the water by the aid of 

 small filaments and only finally settling dow^n and gTow- 

 ing like other plants. Other plant forms never settle 

 down, but are locomotive through life. On the other 

 hand, some marine animals while young are free and 

 movable, but when mature are rooted to one spot, where 

 they live and grow, such as crinoids, corals and sponges. 

 Other organisms are at one stage apparentl}^ animals, 

 while at another stage they appear to be plants. The 

 naturalist of long ago said that the stone grew, the plant 

 grew and lived, while the animal grew, lived and moved. 

 Under our present knowledge this definition or descriiJ- 

 tion would not be suflflcient for some of the lower forms 

 of life. 



There is another thing that may be said concerning 

 life at those early times in the earth's development. 

 Life, as we have seen, probably began while the rocks 

 Avere still so hot as to hold the water at a high tempera- 

 ture. If this was so, we must believe that the evapora- 

 tion was ver}^ much greater then than now, and so the 

 air would have been filled with dense clouds, shutting 

 out a large part of the sunlight which is so necessary to 

 the plant life of the present time. Vegetation in such a 

 condition might have existed without chlorophyll, which 

 is now needed for the sun's chemical action in changing 

 the inorganic material to a suitable form for the living- 

 organism. Protoplasm must have existed before chloro- 

 phyll, as the latter is a modification of the former. The 

 plant and animal in these lower forms are so nearly 

 alike that Huxley has said, "that the problem whether 

 in a given case an organism is an animal or a plant may 



