Microscopical Essays. 



thefe parts, and their feveral fubdi virions, is requifite for thofe 

 who are defirous of forming accurate ideas of thefe little animals, 

 or who wifh to arrange them in their proper clafTes. 



The head is affixed to the thorax by a fpecies of articulation 

 or joint; it is the principal feat of the fenfes, and contains the 

 rudiments of the brain ; * it is furnifhed with a mouth, eyes, an- 

 tennse, a forehead, a throat, and {lemmata. In the greater part 

 of infecls the head is diftin&ly divided from the thorax, but in 

 others it coalefces with it. The head of fome infecls is very 

 large in proportion to their bodies ; the proportion between the 

 head of the fame infecl is not always the fame ; in the caterpillars 

 with horny heads it is generally fmall before they moult or 

 change their fkin, but much larger after each moulting. The 

 hardnefs of the exterior part of the head prevents it's growth 

 before the change, it is confequently, relative to the body, very 

 fmall ; but when the infecl is difpofmg itfelf for the change, the 

 internal fubftance of the head retires inwards to the firft ring of 

 the neck, where it has room to expand itfelf; fo that when the 

 animal quits the {kin, we are furprifed with a head twice the for- 

 mer fize : and as the infeci neither eats nor grows while the head 

 is forming, there is this further circumftanee to be remarked, 

 that the body and the head have each their particular time of 

 growth. While the head expands and grows, the body does not 

 grow at all ; when 'the body increafes, the head remains of the 

 fame fize, without any change. The heads of all kinds of infecls 

 form very pleafmg as well as moll diverfirled objecls for the 



opake microfcope. 



, X 2 The 



* Fabric ius Philofophia Entomologica, p. 18. 



