Microscopical Essays. 



201 



Preparatory to the change, it ceafes to take any food, empties 

 itfelf of all the excrementitious matter that is contained in the in- 

 teftines, voiding at the fame time the membrane which ferved as 

 a lining to thefe and the ftomach. It generally perfeveres in a 

 ftate of reft and inactivity for feveral days, which affords the ex- 

 ternal and internal organs that are under the fkin an opportunity 

 of gradually unfolding themfelves. In proportion as the change 

 into the pupa form approaches, the body is obferved often to 

 extend and contract itfelf ; the hinder part is that which is firft 

 difengaged from the caterpillar fkin ; when this part of the body 

 is free, the animal contracts and draws it up towards the 

 head - } it then liberates itfelf in the fame manner from the two 

 fucceeding rings, confequently the infect is now lodged in the 

 fore part of it's caterpillar covering ; the half which is abandoned 

 remains flaccid and empty, while the fore part is fwoln and dif- 

 tended. The animal, by ftrong efforts, ftill forcing itfelf againft 

 the fore part of the fkin, burfts the fkull into three pieces, and 

 forms a longitudinal opening in the three firft rings of the 

 body; through this it proceeds, drawing one part after the 

 other, by alternately lengthening and fhortening, fwelling and 

 contracting the body and different rings; or elfe, by pufhing 

 back the exuvia, gets rid of it's odious reptile form. 



The caterpillar, thus ftripped from it's fkin, is what we call 

 the pupa, chryfalis, and aurelia, in which the parts of the future 

 moth are inclofed in a cruftaceous covering, but are fo foft, that 

 the flighteft touch will difcompofe them. The exterior part of 

 the chryfalis is at firft exceedingly tender, foft, and partly trans- 

 parent, being covered with a vifcous fluid ; this foon dries up, 

 thickens, and forms a new covering for the animal, capable of 



B b refill:- 



