ON THE NATURE OF ANIMAL LIFE 3 



ences so extraordinary that without the key given to us in the 

 hypotheses of evolution it would have been difficult or impossible 

 to compare animal organs one with another. 



Now we might spend a lifetime (as many men have done) in 

 studying the anatomy of animals, and yet one would really 

 never have studied the animal at all ! It is only when we look 

 at the things that organisms do that we are students of life. In 

 spite of the extraordinary differences of structure (as, for in- 

 stance, between a rabbit and a starfish), there is a remarkable 

 similarity in the functions performed by the organs of the body. 

 Limbs, legs and wings, fins, appendages, tube- feet, etc., are the 

 means of locomotion, and they enable the animals possessing 

 them to run or walk, fly, swim, creep, etc. Teeth, claws, horns, 

 spines, stings, poison-glands, etc., are all weapons which are 

 employed to maim, capture, and kill other animals. The 

 alimentary canal and its glands are the organs of nutrition, the 

 means whereby the animal digests and assimilates its food. 

 Lungs and gills are contrivances whereby oxygen is obtained 

 from the atmosphere, or the sea- water, and the heart and blood- 

 vessels are the mechanism by means of which the oxygen, and 

 also the digested foodstuff, are distributed to all parts of the 

 body. Eyes, ears, nose, tongue, feelers, etc., are the apparatus 

 of sensation, and it is by means of these that the animal becomes 

 aware of the changes that occur in its environment. 



Add to all these things the multitudinous contrivances by 

 means of which animals reproduce, bear offspring, and nourish 

 and cherish the latter. 



Structure and Function. Evidently, then, structure varies 

 in a remarkable degree, but the things that animal structures 

 or organs do are very much the same in spite of the structural 

 or anatomical differences. Limbs, wings, fins, appendages, etc., 

 are the means whereby the animal moves, distributes itself over 

 the world, seeks its prey, or avoids its enemies ; and teeth, claws, 

 etc., are its weapons the means of defence and aggression. 

 These organs, with the alimentary canal and its glands, enable 

 the organism to catch and kill and digest its food. All modes 

 of reproduction, whether sexual or asexual or parthenogenetic, 

 have the same purpose and effect that of the perpetuation of 

 the race. Obviously, then, it is not structure that is the 

 essence of animality, for structure is only the means to various 

 ends. 



