55 [ 475 J 



together. These pieces are more distinct in some insects than in others, 

 hut they can always he distinguished hj' impressed lines upon the sur- 

 face called sutures. The three pieces of the thorax are distinguished as 

 the fore-thorax, the middle-thorax, and the hind-thorax ; or, in scientific 

 language, the pro-iliorax, the meso-fhorax, and the meta-tliorax. In the 

 Coleoptera the pro-thorax is very large, and forms the large ujiper part, or 

 shiehl, to which we usually give the general name of thorax. In this order 

 of insects, the meta-thorax is mvisible above, and the only part of the 

 meso-thorax seen from above is the triangular piece between the bases 

 of the elytra, called the scutellum. 



lu many insects [Hymenoptera and Le^yidoptera) the pro-thorax is 

 much reduced in size, and forms only a narrow rim, which is usually 

 called the collar. 



The under side of the thorax is called the sternum or breast jilate . 

 Each of the three divisions of the thorax has its sternum, designated 

 respectively as the pro-, meso- and meta sternum. In many insects, 

 and especially the Coleoptera, each section of the sternum is divided 

 by sutui'es into a middle piece or sternum proper, and a side iiiece, called 

 the episternum. These parts will be described more particularly in treat- 

 ing of the Coleoptera. 



The appendages of the thorax are the organs of motion, namely, the 

 wings and the legs. 



The Wings. — The great majority of insects have four wings. The ante- 

 rior pair are attached to the upper part of the meso-thorax, and the 

 l^osterior pair to the meta thorax. 



The wings are thin, membranous, transparent organs, in some cases 

 folded when at rest, and supi)orted by ribs or veins running across them. 

 These veins are found to correspond in their number and complexity to 

 the rank of the insect in the scale, and from the ease with which they 

 can be seen, they furnish admirable characters for the purj^oses of class- 

 ification. In some insects, such as the grass-hoppers, the fore-wings are 

 thicker and less transparent than the hinder pair, and have nearly the 

 consistency of parchment; and in one large order- of insects, the Coleop- 

 tera or beetles, the fore-wings become converted into the hard opaque 

 pieces, known as the elytra or wing-cases. The elytra take no part in 

 flight, but serve only to cover and protect the hinder or true wings, 

 which are folded under them when at rest. 



In one large order, the insects have but two wings, and are named 

 from this character Biptera.; or two-winged insects. In these insects 

 the place of the hind- wings is supplied by a pair of little knobbed ap- 

 pendages called halteres or poisers. 



There are a few exceptional cases of two- winged insects in some of 

 the other orders — for example, some of the smaller Day-flies {U])hem- 

 erw) in the order ISTeuroptera, and the males of the Bark- lice {Coccidw) 

 in the order Homoptera. 



