24 AN INTRODUCTION TO ZOOLOGY. 



5. It has to fee]. 



6. It has to move. 



The plant has to do some of these things as well as 

 the animal ; but the plants unless we may give the 

 Sensitive Plant and some others the benefit of a 

 doubt, has not to feel ; and, with similar exceptions, 

 a plant has not to move. These things that have to 

 be done, so long as the organism continues to live, we 

 call its functions. The first four are vegetative func- 

 tions ; the two latter are animal functions. An animal 

 that consists of one cell can do all these things ; we 

 may be rather sceptical about its feeling, but still the 

 creature behaves as if it did, when one watches it 

 under the microscope. It feels its way along ; it feels 

 a grain of material that happens to touch it, and 

 throws out a " feeler " to touch it. About the move- 

 ment, anyway, there is no question. 



But when an animal consists of many cells instead 

 of one, then these various duties, or functions as they 

 are called, are portioned out according to the principle 

 of the " division of labour." We have all been taught 

 what the " division of labour " means, by an often- 

 quoted example regarding the making of pins. In- 

 stead of one man doing all the required processes, 

 and taking such and such time to do it, now, we 

 were told, by the "division of labour" plan, one 

 man makes the head, another man makes the pin, 

 .and another fastens them together, thereby savin"- 

 all the time that used to be expended by the one man 

 in changing from one process to the other, besides 



