56 EVOLUTION 



of these very lowly organisms in a special group, the 

 Monera, below the level of the distinction between 

 animal and plant. However that may be, the plant and 

 animal must have diverged from a common stock at a 

 very early date. If an organism can feed on inorganic 

 matter it has little or no need to travel, and no stimulus 

 to develop organs of sense-perception. On the other 

 hand, the animal must move about in search of its rarer 

 food (or else have long lashes to beat the water and 

 bring the food to it), and an increasing degree of sensitive- 

 ness will be a great advantage to it in its travels. Thus 

 we get the broad lines of the evolution of the plant and 

 the animal. The one will become (generally) an inert 

 and motionless structure, sucking food from the soil 

 where it is cast, and at a later stage from the air about 

 it, and growing a thick, tough skin, because it needs no 

 sensitiveness to the waves of light and other stimuli. 

 The other, the animal, will specialise on organs of 

 locomotion and sensitiveness, and pass on through the 

 fish stage to that of the higher land animal. 



The evolution of the plant is not only of less general 

 interest than that of the animal, but it is more obscure, 

 and must be treated here very briefly. We need, in 

 fact, do little more than describe the various kinds of 

 plants that make their successive appearance in the 

 geological record. In the Cambrian strata the botanist 

 claims to find the first traces of early plant life. These 

 fossils (Eophyton and Oldhamia) are by no means 

 undisputed, but they are (if vegetal) of the same general 

 character as those in the Silurian period, and may be 

 taken to represent the lowest type of plant preserved in 

 the rocks. From what we have seen above, it will be 

 expected that they by no means belong to the lowest 

 groups of living things. They are large plants of the 

 seaweed type, and imply that innumerable generations 



