THE STUDY OF ENTOMOLOGY 215 



divided into three segments called respectively the 

 prothorax, mesothorax, and metathorax. The abdo- 

 men is composed usually of ten rings or segments, 

 and has at the tail end various appendages such as 

 the setae or tails of the EphemeridcB and the male 

 genitalia in most insects. 



Respiration takes place by means of tracheae, a 

 system of tubes distributed throughout the body, 

 opening externally by orifices in the sides of the 

 abdomen. There are invariably six legs attached in 

 pairs to the under or ventral side of each segment 

 of the thorax. A pair of antennae are placed on 

 the head. Some have four wings, some two, and 

 some none ; the wings are always attached to the 

 upper or dorsal side of the thorax by strong muscles 

 and ligaments. The wings, if there are two pairs, 

 are attached, the fore wings to the mesothorax and 

 the hind wings to the metathorax. If there should 

 be only one pair of wings it is generally attached to 

 the mesothorax. 



The skin is the hardest and most solid portion 

 of an insect's anatomy, and is composed of a 

 substance called chitin, which is tough, flexible and 

 horny. Some insects subsist on solid food and are 

 called mandibulata (jawed), others live on fluids and 

 are called haustellata (suckered). 



Most insects can see, and have two kinds of 

 eyes : Ocelli (single eyelets), three or a pair ; and 

 a pair of oculi (eyes), formed of eyelets touching one 

 another in faceted or compound eyes but less 



