Microscopical Essays. 209 



the affiftarice of glaffes, and are confequently a* proper fubje& for 

 the microfccpe ; we fhall felecl from a great variety, a few 

 inflances, to animate the reader in thefe refearches. 



Some caterpillars, towards the time of their change, fufpend 

 themfelves from the branch of a tree, with the head downwards ; 

 in this pofition they afTume the pupa form, and from thence im~ 

 merge a butterfly or moth. In order to fufpend itfelf in this po- 

 fition, the in feci: covers with threads that part of the branch 

 from which it means to fufpend itfelf ; it places thefe in different 

 directions, and then covers them with other threads, laying on 

 feveral fucceffive thicknefies, each new layer being final ler in fize 

 than that which preceded it; forming, when finifhed, a little 

 cone or hillock of filk, as will be found when examined by the 

 microfcope. The caterpillar hooks itfelf by the hinder feet to 

 this hillock ; and when it has found, by feveral trials, that it 

 is ftrongly fixed thereto, throws itfelf forward, letting the body 

 fall with the head downwards. Soon after it is thus fufpended, 

 it bends the fore . part of the body, keeping this bent 

 pofture for fome time ; then ftraitening the body, again in a little 

 time bending it, and fo on, repeating this operation till it has 

 formed a flit in the fkin upon the back ; part of the pupa foon 

 forces itfelf through this, and extends the flit as far as the 

 laft cru ftaceous feet; the pupa then forces upwards the fkin, as 

 we would pufh down a flocking, by means of it's little hooks and 

 the motion of the body> till it has flipped it off to that part from 

 which the caterpillar had fufpended itfelf. But the pupa has ftill 

 to difengage itfelf from this fmall packet, to which the ex u via is 

 now reduced : here the obferver will find himlelf interefted for 

 the little animal, anxious to learn how the pupa will quit this 



C c fkin, 



