196 ZOOLOGT. 



be distinctly determined, it is divided into Tliorax, Scutel- 

 lum, and Sternum. The Thorax is various in its shape, as 

 is the back or upper part of the breast or Sternum. The 

 Scutellum is the posterior part of the Thorax, frequently of 

 a triangular shape, and is divided from the Thorax by a 

 suture, very conspicuous in many of the Coleopterous 

 Insects. 



The Abdomen is the posterior part of the body, and is 

 composed of a number of annular sections or rings, which 

 serve to contract wr lengthen it as occasion may require ; the 

 last joint terminates in the tail. The Spiracula or Breathing 

 apertures, are situated on each side of every segment or arti- 

 culation of the abdomen, and if these be closed with oil or 

 other unctious substance, it mostly proves fatal to them : as 

 before observed, some particular kinds will survive days after 

 this part is entirely removed, yet in these, if the spiracula be 

 stopped up, they soon expire. 



The limbs of Insects consist of three principal divisions ; 

 the first or upper joint Femur or Thigh ; the second joint 

 Tibia or Leg ; the third, which consists of several articula- 

 tions, is called Tarsus or Foot ; and in some kinds the foot 

 is furnished with Unguis or Claws, which are mostly double. 

 Most of those Insects included in the Order Diptera, are pos- 

 sessed of two small protuberances or bladders, one situated 

 under each wing, which are termed Halteres or Poisers, and 

 are supposed to assist in balancing the Insects in their flight. 



The larger number of Insects are annual, their whole life 

 terminating in the space of one year or less ; many not sur- 



