THE SIMPLER ORGANISMS 



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. 



