236 



Microscopical Essays. 



An infecl: that muft caft off it's exuvia, or moult five times be- 

 fore it attains the pupa ftate, may be confidered as compofed of 

 five organized bodies, inclofed within each other, and nourifhed 

 by common vifcera, placed in the center : what the bud of the 

 tree is to the invifible buds it contains, fuch is the exterior part 

 of the caterpillar to the interior bodies it conceals in it's bofom. 



Four of thefe bodies have the fame effential ftruclure, namely, 

 that which is peculiar to the infecl in it's larva or caterpillar ftate : 

 the fifth body is that of the pupa. The refpedive ftate of thefe 

 bodies is in proportion to their diftance from the center of the 

 animal ; thofe that are fartheft off have moft confidence, or un- 

 fold themfelves fooneft. 



When the exterior body has attained it's full growth, that in- 

 terior one which is next in order is confiderably unfolded ; it is 

 then lodged in too narrow a compafs, therefore it ftretches on all 

 fides the {heath which covers it ; the veffels which nourifh the ex- 

 ternal covering, being broken by this violent diftenfion, ceafe to 

 aft, the fkin wrinkles and dries up ; at length it opens, and the 

 infecl is c loathed with a new fkin, and new organs. 



The infecl; generally fafts for a day or two preceding each 

 change ; this is probably occafioned by the violent ftate in which 

 it then is, or it may be neceffary to prevent obftruclions, ckc. let 

 this be as it may, the infecl is always very weak after it has: 

 changed it's fkin, the parts being as yet affecled by the exertions 

 they have gone through. The fcaly parts, as the head and legs, 

 are almoft entirely membranaceous, and imbrued with a fluid 

 that infinuates itfelf between the two (kins, and thus facilitates 



their 



