EXPANSION OF PERFECT INSECTS. 339 



Some species of flies have their wings shortened 

 very considerably in the pupa state by zigzag or 

 transverse folds; so that, when newly evolved, it 

 might be supposed, from their moist and crumpled 

 appearance, that they could never become so fine, 

 gauzy, and translucent, as they are actually seen to 

 do. This will be better understood from the above 

 figures than by description. ^ 



We have taken the preceding examples of expan- 

 sion of the wings from those insects in which these 

 are more or less transparent, and consequently the 

 branching of the tubes (nervures) through them is 

 more obvious than in moths and butterflies, in which 

 the wings are covered with feathery scales. It is, 

 however, less rare to see the latter transformed than 

 the former, from the greater facility of rearing them, 

 and on that account it may be proper to take some 

 notice here of their transformation. We cannot in 

 this find better guides than Swammerdam and the 

 celebrated Italian anatomist, Malpighi, in his account 

 of the silk-worm. "At length," says the latter, 

 " within four days, the heart (dorsal vessel) of the 

 silkworm continues moving slowly, and the body 

 growing bigger, having thrown off the outward skin 

 like a slough, the pupa appears a new creature. The 

 throwing off the old and assuming this new form, is 

 completed in the space of one minute and ten seconds; 

 and it is thus done, as I chanced to see it. The 

 motion of the heart {dorsal vessel) is very quick at 

 first, and the whole frame of the body appears con- 

 vulsed ; so that the several circular folds of the 

 segments emerge, and by the transverse contraction 

 of the sides, the external skin is separated from the 

 inner ; hence, upon making an effort, and thrusting 

 the body, which now appears particularly thick, 

 towards the head, the skin is driven backward and 



