362 ON THE STUDY OF ZOOLOGY 



haunts, and it will greedily devour it, tearing and crushing 

 the flesh by means of its multitudinous jaws. 



Suppose that we had known nothing of the lobster but as 

 an inert mass, an organic crystal, if I may use the phrase, 

 and that we could suddenly see it exerting all these powers, 

 what wonderful new ideas and new questions would arise 

 in our minds I 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 beauti- 

 fully 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 suddenly to kill one of 

 these animals and to take out all the soft parts, I should 

 find the shell to be perfectly 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 perceive 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 spon- 

 taneous motion in it ; but on pinching any portion of the 

 flesh, I should observe that it underwent a very curious 

 change each fibre becoming shorter and thicker. By 

 this act of contraction, as it is termed, the parts to which 

 the ends of the fibre are attached are, of course, approxi- 

 mated ; and according to the relations of their points of 

 attachment to the centres of motions of the different rings, 

 the bending or the extension of the tail results. Close 

 observation of the newly-opened lobster would soon show 

 that all its movements are due to the same cause the 

 shortening and thickening of these fleshy fibres, which are 

 technically called muscles. 



Here, then, is a capital fact. The movements of the 

 lobster are due to muscular contractility. But why does 



