158 WHAT MAY BE LEARNED FROM EOZOON 



those animals which subsist in complex communities, and 

 which aggregate large quantities of mineral matter in their 

 skeletons. So true is this that up to the present time all the 

 species of Protozoa and of the animals most nearly allied to 

 them are aquatic. Even in the waters, however, plant life, 

 though possibly in very simple forms, must precede the 

 animal. 



Let humble plants, then, be introduced in the waters, and 

 they would at once begin to use the solar light for the purpose 

 of decomposing carbonic acid, and forming carbon compounds 

 which had not before existed, and which, independently of 

 vegetable life, would never have existed. At the same time 

 lime and other mineral substances present in the sea water 

 would be fixed in the tissues of these plants, either in a minute 

 state of division, as little grains or Coccoliths, or in more solid 

 masses like those of the Corallines and Nullipores. In this 

 way a beginning of limestone formation might be made, and 

 quantities of carbonaceous and bituminous matter, resulting 

 from the decay of vegetable substances might accumulate on 

 the sea bottom. Now arises the opportunity for animal life. 

 The plants have collected stores of organic matter, and their 

 minute germs, along with microscopic species, are floating 

 everywhere in the sea. The plant has fulfilled its function as 

 far as the waters are concerned, and now a place is prepared 

 for the animal. In what form shall it appear ? Many of its 

 higher forms, those which depend upon animal food or on the 

 more complex plants for subsistence, would obviously be un- 

 suitable. Further, the sea water is still too much saturated 

 with saline matter to be fit for the higher animals of the waters. 

 Still further, there may be a residue of internal heat forbidding 

 coolness, and that solution of free oxygen which is an essential 

 condition of existence to the higher forms of Hfe. Something 

 must be found suitable for this saline, imperfectly oxygenated, 

 tepid sea. Something, too, is wanted that can aid in introduc- 



