CHAPTER IV. 



GENERAL PRINCIPLES CONCERNING ANIMALS. 



Animals in general are living beings with very curious properties, 

 well calculated to astonish us and excite our study. These beings, 

 infinitely varied in shape, organisation, and faculties, are capable of 

 moving themselves or some of their parts without the impulse of any 

 movement from without. Their irritability is due to an exciting 

 cause which in some originates from within, while in others it comes 

 entirely from without. Most of them possess the property of loco- 

 motion, and all have parts that are highly irritable. 



We find that in their movements some crawl, walk, run or leap ; 

 others fly, rising into the atmosphere and passing through wide spaces ; 

 others again five in the waters and swim about there freely. 



Animals are not, Uke plants, able to find close by within their reach 

 the material on which they feed ; and the predatory animals are 

 actually obUged to go forth and to hunt, chase and seize their prey. 

 It was necessary therefore that they should have the power of motion 

 and even of locomotion, in order to procure the food which they 

 require. 



Moreover, those among animals which multiply by sexual repro- 

 duction are not hermaphrodite enough to be sufficient to themselves. 

 Hence it was farther necessary that they should be able to travel 

 about for the purpose of effecting acts of fertilisation, and that the 

 environment should provide facilities for it to those which, like 

 oysters, cannot change their position. 



Thus the needs of animals have endowed them with the property 

 of moving parts of their bodies, and of carrying out locomotion which 

 subserves their own survival and that of their races. 



In Part II. we shall enquire into the origin of this extraordinary 

 faculty, as of the other important faculties found among them ; 

 but it suffices at present to draw attention to certain obvious 

 points. 



