212 THE STUDY OF ZOOLOGY vii 



minds ! The great new question would be, " How 

 does all this take place ? " the chief new idea would 

 be, the idea of adaptation to purpose, — the notion, 

 that the constituents of animal bodies are not 

 mere unconnected parts, but organs working 

 together to an end. Let us consider the tail of 

 the lobster again from this point of view. 

 Morphology has taught us that it is a series 

 of segments composed of homologous parts, 

 which undergo various modifications — beneath 

 and through which a common plan of formation 

 is discernible. But if I look at the same part 

 physiologically, I see that it is a most beautifully 

 constructed organ of locomotion, by means of 

 which the animal can swiftly propel itself either 

 backwards or forwards. 



But how is this remarkable propulsive machine 

 made to perform its functions ? If I were sud- 

 denly to kill one of these animals and to take out 

 all the soft parts, I should find the shell to be per- 

 fectly inert, to have no more power of moving 

 itself than is possessed by the machinery of a mill 

 when disconnected from its steam-engine or water- 

 wheel. But if I were to open it, and take out the 

 viscera only, leaving the white flesh, I should per- 

 ceive that the lobster could bend and extend its 

 tail as well as before. If I were to cut off the 

 tail, I should cease to find any spontaneous motion 

 in it ; but on pinching any portion of the flesh, 

 I should observe that it underwent a very curious 



