EXPANSION OF PERFECT INSECTS. 339 



Some species of flies have their wings shortened 

 very considerably in the pupa state by zig-zag or trans- 

 verse 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 trans- 

 lucent, as they are actually seen to do. This will be 

 better understood from the above figures than by de- 

 scription. 



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 branch- 

 ing of the tubes (nervures) through them is more obvi- 

 ous 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 bet- 

 ter 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 silk-worm 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 

 convulsed; so that the several circular folds of the seg- 

 ments emerge, and by the transverse contraction of the 

 sides, the external skin is separated from the inner; 

 hence, upon making an eflhrt, and thrusting the body, 

 which now appears particularly thick towards the head, 

 the skin is driven backward and downward; and the 



