10 DESCRIPTION OF PARTS. 



Sverce pleura and periplevm; the latter supports the halteresax powers in dipterous in- 

 s, The thorax Invariable supports six legs. The wings are sometimes wanting, when 



the in^ti-t i- said to be apterous : those with two wings art- dipterous; and those with lour, 

 totrapttrous- The superior wings are provided with an articulating socket, which is formed 



ill part bj the organ called the scapula : they lie cli.se upon the sternum; they constitute 

 the second principal portion of the mesothorax, lying one on each side in front. Another 

 distinct portion of the mesothorax Is themesosterntan: it lies upon the under side, opposite 

 the UBSOnotum ; in its area the middle legs are articulated. The niesosternum is not equal- 

 ly developed in all orders of insects : it is most perfect in the Coleoptera and Orthoptera; 

 the donal portion has received the aaJDS of metanotum, quadrangular in form, and emargi- 

 uate in front. 



The parts supported l>y the thorax are the wings and legs; and, as has been observed 

 already, the latter are invariably six in number, and never wanting. The wings are variable 

 iu uumber, in form and in substance ; and upon the variability iu form and substance, the 

 order< are composed. Thus those with four wings are termed tetrapterous; those with two, 

 dipterous; and those with none, apterous. The anterior pair in Tetraptera is attached to the 

 Dtesothorax : this pair is also sometimes called the superior pair, while the pair attached 

 to the tnetathorax is called the posterior or inferior pair. The pair which is wanting in the 

 Diptera. is the posterior pair. 



It has been said that the wings differ in form and substance. Nature, however, preserves 

 rigorously the symmetry of parts. In Coleoptera, the anterior wings differ from the posterior 

 both in substance and form. The substance of the first is leathery, more or less rigid, and 

 horny : their form is various, but adapted to the dorsum or back of the insect ; while the 

 posterior are membranous, flexible and elastic, and capable of being folded beneath' the 

 anterior wings. In another order of Tetraptera the wings are similar in form and substance, 

 and of equal size : these insects have received the name of Neuroptera. Where, however, 

 in tetrapterous insects, the posterior wings differ in size, but preserve the fqrm and sub- 

 stance of the anterior, the order is called Hymenoptera. Examples of Neuroptera are the 

 ■ allies; of Hymenoptera, the common honey-bee, wasp, etc. In flight, the rigid an- 

 terior wing of the Coleoptera is of little use : it serves to protect the membranous wing 

 and abdonu-n when at rest. Hence it is that the flight of beetles is short, and sustained 

 evidently with much more labor than that of dragon-flies or honey-bees. The insects whose 

 wings are four, and covered with scales, are called from this List circumstance Lepidoptcra. 



It i- proper here to remark, that while there is a great dissimilarity between the anterior 

 wing of a beetle and that of a dragon-fly, yet we are not to suppose that the difference is 

 effected by a sudden leap : there is really a gradation in substance. We have insects whose 

 anterior wing- an- intermediate in this respect, both in substance and form. Thus the com- 

 mon grasshopper ha- an anterior wing which i- between leathery and membranous, and is 



