ig6 Microscopical Essays. 



and fheaths of the anterior limbs, and in general all that is vifible 

 of the caterpillar. 



The new organs were under the old ones as in a Iheath, fb 

 that the caterpillar effects the changes by withdrawing itfelf from 

 the old fkin, when it finds itfelf lodged in too narrow a compafs. 

 But to effect this change, to pufh off the old covering, and bring 

 forwards the new, is a work of labour and time. Thofe cater- 

 pillars who live in fociety, and have a kind of neff or habitation, 

 retire there to change their fkin, fixing the hooks of the feet,, 

 during the operation, firmly in the web of their nelL Some of 

 the folitary fpecies fpin at this time a (lender web, to which they 

 affix themfelves. A day or two before the critical moment ap- 

 proaches, the infect ceafes to eat, and lofes it's ufual activity - 

 in proportion as the time of change approaches, the colour of the 

 caterpillar becomes more feeble, the fkin hardens and withers,, 

 and is foon incapable of receiving thofe juices by which it 

 was heretofore nourilhed and fupported. The infect may now 

 be feen, at diflant intervals, to elevate it's back, and firetch itfelf 

 to it's utmofl extent ; fometimes to lift up the head, move it a 

 little from fide to fide, and then let it fall again ; near the change, 

 the fecond and third rings are feen to fwell eonfiderably ; by thefe 

 internal efforts the old parts are ft retched and diflended as much 

 as poffible, an operation which is attended with much difficulty, 

 as the new parts are all weak and tender. However, by repeated' 

 exertions, all the vefFels which conveyed the nourilhment to the 

 exterior fkin are difengaged, and ceafe to aft, and a flit is made 

 ' on tne back , generally beginning at the fecond or third ring ; the 

 new Ikin may now be juft perceived, being difling mined by the 

 frefhnefs. and brightness of it's colour; the caterpillar then prefles 



