Microscopical Essays. 



Serrata, having the" external margin -edged with teeth or 

 notches, j 



Spin os a, when the exterior furface is covered with fmall fharp 

 points. 



Scabra, when it is very rough. 

 Striata, marked with (lender longitudinal furrows. 

 Porcati, having (harp longitudinal ridges. 

 Sulcati, wkh deep furrows. 



Hemelytra, when the cafes are neither fo hard as the elytra, 

 nor fo delicate as the tranfparent wing. 



Under the wings of moft infefts, which have only two, there 

 is a fmall head placed on a ftalk, frequently under a little 

 arched fcale ; thefe are called halteres, poifers; they appear to 

 be rudiments of the hinder wings : it has been fuppofed that they 

 ferve to keep the body in equilibrio when the infecl: is flying. 



The bodies of infects are covered with a hard fkin, which an- 

 fwers the purpofe of an internal fkekton, and is one of the dif- 

 tinguiming characters of an infecl:. All quadrupedes, birds, and 

 fifties, have an internal fkeleton of bones to which the mufcles 

 areiixed; but the whole interior body of an infecl is compofed 

 of foft flelh, and the mufcles are affixed to the exterior ikeleton 



♦or 



