THE SIMPLER ORGANISMS 



91 



Pi 



H 



< 



O 

 Pi 



Income 



CO^ from 

 the air 



Mineral 

 salts in 

 solution 



Outgo 



Free 

 oxygen 



jCO, 

 |H,0 



The Green 



Plant 



Cell 



Radiant 



energy of 



the sun 



Chemical 



energy 



of free 



oxygen 



Heat, inove 

 ments of pro- 

 toplasm, &c. 



Chiefly dis- 

 appears in 

 syntheses 

 organic 

 compounds, 

 becoming 

 potential 



of 



Income 



Free 



oxygen 



Proteins 

 Carbohy- 

 drates and 

 fats in food 

 H.O & salts 



Outgo 



CO3 

 H/J 



Urea and 



other 



nitrogen 



compounds 



The 



Animal 

 Cell 



Potential 



chemical 



energy 



of the food 



and of free 



oxygen 



Movements, 

 heat, &c. 



(A Httle is 



lost in 



nitrogen 



waste) 



III. SOME INTERMEDIATE AND UNDIFFERENTIATED FORMS. 



The typical algae and protozoa studied thus far, conform 

 to our general notion of plant and animal, derived from 

 contact with the higher, familiar forms of life. The green 

 color of the plant and the free movement and foraging 

 habit of the animal seem at first to mark out naturally two 

 distinct groups; among the higher forms there is no diffi- 

 culty about distinguishing between plant and animal. It 

 is easy to tell a dove from a daffodil ; it is not hard to tell a 

 green alga from, a free swimming gray protozoan ; but there 

 are among the lower organisms some that do not clearly 

 show even the broad distinctions of the preceding diagram, 

 and some that so combine the characters of the two groups 

 that one may not say with assurance whether they are 

 plants or animals. 



