THE THORAX. 91 



ORGANS OF MOTION UPON THE THORAX. 

 A. The Wings. 

 79. 



The organs of motion are of two kinds, either WINGS (aloe}, or LEGS 

 (pedes~). 



The wings, generally four in number, are placed, as we have already 

 seen, upon the second and third segments of the thorax, and united to 

 it by means of joints or an articulatory membrane. They always 

 consist of a double membrane, which is traversed by corneous VEINS or 

 RIBS (jieurcg, vence, costte^), and by means of which they are held 

 expanded. This, their general structure, suffers a variety of modifi- 

 cations in the different orders, which may be comprehensively repre- 

 sented in the following table : 



I. Four wings. 



1. All of similar structure and membranous : 



A. Of equal size. Neuroptera (with the exception of 



the families of the May-flies), as well as the families 

 of the Libellulina and Termitina. 



B. Of unequal size. Hymenoptera, Lepidoptera, Phryga- 



neodea, the remaining Dictyotoptcra, and many Hemi- 

 ptcra homoptera. 



2. The anterior corneous or pcrgamentaceous, the posterior 



membranous : 



A. The anterior corneous. 



a. Entirely corneous, Coleoptera. 



b. Half corneous, half membranous, Hemiplera 

 heteroptera. 



B. The anterior pergamentaceous. Orihoptera, and some 



Hemiplera homoptera. 



II. Two membranous wings. Dipicra. 



The general observations which we purpose here introducing upon 

 the wings, will merely refer to their number, situation, form, and 

 clothing. The inquiries into their structure, import, and purpose, 

 belong to other divisions of this work, and will, consequently, remain 

 untouched upon here. 



Very little is to be said upon their number ; sometimes, and indeed, 

 in certain genera and species of almost every order, they are wholly 



