CLASS I. INSECTA. 



SUB-CLASS I.— INSKCTA PROPER. 



Mg. SIS- 



General Characteristics. — Insects (cut into) have the 

 body divided into three portions — 

 head, thorax, and abdomen. From 

 the head proceed two little stems 

 called antennm, which are sup- 

 posed to be organs of touch, and 

 perhaps also of sound. The thorax 

 is composed of three rings, each 

 bearing a pair of legs, and the 

 second usually, and the third some- 

 times, in addition, a pair of wings. 

 The abdomen has typically eleven 

 segments. 



Respiration is effected by a 

 number of breathing apertures, in 

 each side of the body, that open 

 into tubes (trachem), formed of a 

 spirally-roUed, cartilaginous fila- 

 ment, communicating freely with 

 one another, and, in their last 

 ramifications, penetrating the sub- 

 stance of the organs. In the wings, where this 

 network of horny tubes is particularly apparent, 

 they are called veins and veinlets. Inclosing them 

 is a larger tube filled with blood, which is aerated 

 by absorbing air through the membranes of the 

 tubes. 



The Digestive Apparatus is very complicated, 

 consisting of mandibles, gullet, stomach, crop, 

 gizzard, intestines, etc. 



The Eyes of most insects are compound, consisting of a 

 multitude of small eyes* (facets), each perfect in itself; but 



Anatomy of External Slceleton 

 of a Winged Insect. 



Tracliea of 

 an Insect. 



* The number of these facets is often enormous— in certain kinds of beetles it 

 pxceeds twenty-five thousand, and in the common house-fly it is four thousand. 



