METAMORPHOSIS. 75 



A few words as to the cause of metamorphosis. In even- 

 organized being we trace these three tendencies ; firsts to 

 haA-e its component parts become unfit for their fimctions ; 

 secondly^ to throw off or discard all parts thus becoming 

 unfit ; thirdly, to form, create, or supply, fresh portions in 

 lieu of those thus thrown off. In tliis threefold tendency 

 we shall find a solution of all the mysterious changes we 

 behold in animals and vegetables ; whether we regard the 

 loosening of teeth, the shedding of hair, the moulting of 

 feathers, the casting of skins or the falling of leaves. This 

 change of substance is generally obsei^vable in the exterior 

 covering, but in man, the most perfect animal, it is more 

 obvious in the bones. Numberless experiments prove that 

 the substance of bones is continually changing ; some por- 

 tions are constantly undergoing absorption, others secre- 

 tion. Thus certain particles of matter escape to fulfil other 

 ends, while new particles, introduced as ahment for the 

 system, are mixed with its fluids and msh to supply the 

 place of those which have escaped. 



All animals possessing an internal skeleton or frame of 

 bones similar to that of man, like man also exhibit this ten- 

 dency more strongly in their bones than in any of their less 

 solid parts. Now in insects the skeleton is external, and 

 exactly comparable to an indurated skin ; yet it serves the 

 same purpose as the skeleton of other animals. Tliis dif- 

 ferent situation of the skeleton accounts in great measure 

 for the difference in the effects of the tendency to change, 

 for while in the larger animals these efiects are concealed 

 fi-om view, and are going on without any consciousness on 

 the part of the animal, in an insect they are very apparent, 

 and fi'om their locality temporarily detract from its present 

 well-being, always causing sickness, and often death. 



There are many animals, as crabs, lobsters, &c., which 

 resemble insects in the possession of an external skeleton. 



