INSECTS : THEIR BREATHING ORGANS. 107 



suitable object for investigation : besides which, there 

 are the beautiful and interesting points in the details of 

 its structure, which I have been endeavouring to bring 

 before you. 



Not less interesting and remarkable is the change in 

 the position of the spiracles, which takes place as soon as 

 this grub arrives at the pupa or chrysalis state. The skin 

 of the active, fish-like larva splits down the back, and out 

 presses an equally active little monster; which, if you did 

 not know it, you would never think of connecting with the 

 grub from which it has proceeded; so totally different is 

 it in form, in structure, and in motions. 



We shall easily find some in our basin that have passed 

 into this stage. Yes, here is one, which will please to 

 take its place in the glass trough with its younger brothers. 

 How strange the transformation ! It reminds us of a 

 lobster, though, of course, the resemblance is only appa- 

 rent. With the naked eye we see that the thorax is 

 greatly enlarged, not only actually, but proportionally ; 

 that it forms an oval mass, occupying some five-sixths, at 

 least, of the entire animal ; the rest, apparently, being 

 taken up by a slender, many-jointed abdomen, which 

 curves round the great thorax, and, bending under it, 

 ends in a very delicate, transparent swimming-plate. It 

 is this curving abdomen, with its terminal swimmer, and 

 its backward strokes in swimming, that constitute the 

 resemblance to a prawn or lobster. 



If we now bring a low power with reflected light to bear 

 on it, we shall see the progress the animal has made in 

 this its change of raiment. The thorax shows on its 

 sides the future wings, crumpled and folded down, the 

 nervures of which we can discern distinctly. The elegant 

 little head, too, can be well made out ; its eyes now per- 

 fectly marked with the numerous six-sided facets that 

 belong to the matured organs of vision in these creatures; 

 its antenna?, like slender rods, folded down side by side 



