22 CHAPTERS ON EVOLUTION. 



preliminary knowledge of structure, the intelligent appreciation of 

 function, or working, is impossible of attainment. The exact manner 

 in which a watch performs its duties can only be comprehended after 

 an examination of its anatomy or the disposition of its parts. Hence, 

 in living beings, " how life is carried on " is a question only to be 

 answered from the knowledge and by the aid of the considerations 

 which the examination of their structure affords and supplies. 



Summing up the history of the living being in action which 

 physiology writes for us, we may say that three great functions are 

 performed by every animal and by every plant. The living being 

 has first to nourish itself; to provide for the continual wear and tear 

 to which, in the mere act of living and being, its frame is subjected. 

 The first function of Nutrition thus provides for the support of the 

 individual animal or plant. But death is continually thinning the 

 ranks of animal and plant species. As local death, or the decay of 

 the particles of the individual body, is a constant concomitant of 

 individual life, no less true is it that general death is an invariable 

 accompaniment of the life of the race or species. As nutrition the 

 act of taking and assimilating food repairs individual loss, so the 

 function of Reproduction repairs the loss and fills the gaps which 

 death has made in the ranks of the race. New beings, through the 

 exercise of this latter function, are brought into the world to take 

 the place on the stage of life of the actors whose parts in the 

 biological drama have already been played out. 



Lastly, in the exercise of its living powers, the animal or plant 

 is found to possess certain means for acquiring relations of more or 

 less definite kind with its surroundings. An amoeba in its way a 

 mere speck of protoplasm is seen under the microscope to contract 

 its jelly-like body when a food-particle touches its substance ; and, 

 as the result of the contact, the protoplasmic speck engulfs the 

 atom in question and duly assimilates it. But for this property of 

 sensitiveness, the life of the animalcule would be equivalent to the 

 existence of the mineral ; its power of nourishing its frame and of 

 receiving food really depends on its sensitiveness to the outward 

 impressions produced by the chance contact with its body of the 

 external particles on which it feeds. Withdraw from the protoplasm 

 this sensitiveness, and your animalcule would starve. Sensation and 

 a power of acting, like human units of official nature, upon "infor- 

 mation received " through sensation, is a universal attribute of life. 

 Even the fixed plant may, as in the Venus's fly-trap (Dionaa\ 

 develop a more sensitive and elaborate apparatus for the capture of 

 prey than many animals of tolerably high grade ; and in all plants 

 there exists living protoplasm which, as its first characteristic, exhibits, 

 sensitiveness and a power of contraction. A snail, irritated by 

 touching the tip of its tentacles, withdraws into the obscurity of 



