IV.] METAMORPHOSES OF INSECTS. 67 



clature of entomological works (larva state and pupa 

 state) does not apply to it ; and even in the case 

 of Lepidoptera, the change from the caterpillar to 

 the chrysalis and from this to the butterfly is in 

 reality less rapid than might at first sight be sup- 

 posed ; the internal organs are metamorphosed very 

 gradually, and even the sudden and striking change 

 in external form is very deceptive, consisting merely 

 of a throwing off of the outer skin the drawing 

 aside, as it were, of a curtain and the revelation of 

 a form which, far from being new, has been in pre- 

 paration for days ; sometimes even for months. 



Swammerdam, indeed, supposed (and his view was 

 adopted by Kirby and Spence) that the larva con- 

 tained within itself " the germ of the future butterfly, 

 enclosed in what will be the case of the pupa, which 

 is itself included in three or more skins, one over the 

 other, that will successively cover the larva." This 

 was a mistake ; but it is true that, if a larva be exa- 

 mined shortly before it is full grown, the future 

 pupa may be traced within it. In the same manner, 

 if we examine a pupa which is about to disclose 

 the butterfly, we find the future insect, soft indeed 

 and imperfect, but still easily recognizable, lying 

 more or less loosely within the pupa-skin. 



One important difference between an insect and a 

 vertebrate animal is, that whereas in the latter as, for 

 instance, in ourselves the muscles are attached to an 

 internal bony skeleton, in insects no such skeleton 

 exists. They have no bones, and their muscles are 

 attached to the skin ; whence the necessity for the 

 hard and horny dermal investment of insects, so 



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