VARIETY AND UNITY IN LIFE 



2:^ 



outside stimulus hold in all the organic world. We call animals 

 and plants "organic" because they are made up of organs, 

 cells, and tissues so grouped that like structures perform like 

 functions. We could not use 

 a generic term like organic, 

 were it not for the structural 

 resemblances existing in each 

 individual in great groups of 

 organisms. All organisms 

 have the impulse to repro- 

 duction. All are forced to 

 make concession after con- 

 cession to their surroundings 

 and in such concessions prog- 

 ress in life consists. At 

 last each organism or each 

 alliance of organisms is dis- 

 solved by the process of 

 death. 



The unity in life is then 

 not less a fact than the 

 diversity. However great 

 the emphasis we lay on in- 

 dividuality or diversity, the 

 essential unity of life must 

 not be forgotten. Whatever 

 solution we may find to the 

 prol^lem of the origin of 

 species, must also explain 

 why species and individuals 

 may be so much alike in all 

 large details of structure. 

 To know the origin of species 

 we must also know why 

 species admit of natural 

 classification. Why is variety 

 in life based on essential 



unity? 



From the fundamental unity of the species of to-day. \u' 

 may infer the similar unity of species in past time. Trom tlie 

 knowledge of variety in unity comes the likenimr of species of 



Fig. 13.— Starfish walking. (.\ft<*r 

 Marey.) 



