DESCRIPTION OF PARTS. 11 



elongated very frequently beyond the body. This is the characteristic of the order Orifio- 

 ptem of systematic writers ; and in this order, the wing grows with the body of the insect. 

 There is another modification of the anterior wing, which seems to arise from an arrest of 

 development, as the organ acquires scarcely half its usual length : tliis modification has 

 served to establish the order Hemiptera of authors. 



A still more beautiful modification of the wing of the insect is found in butterflies and 

 moths. In these the membrane and network, constituting the frame and foundation-work 

 ' of the organ, are covered with a mealy substance, or what appears to the unassisted eye as 

 such. This substance, however, is a scale of a beautiful workmanship, of a variable form 

 and size in different insects, and in different parts of the wing of the same insect : they 

 are beautiful objects for the microscope. Rude handling immediately destroys the beauty 

 of the wing, by detaching these scales, and leaving the membrane beneath naked and 

 broken. 



The wing, anatomically considered, is composed of two parts : the nervures, and ??ie»z- 

 brane. The former are likened unto ribs T which start from the anterior angle, and branch 

 in various ways as they pass to the posterior margin. They give strength to the organ, and 

 serve an important purpose in supporting and staying the outstretched membrane. The 

 nervures are not, as might at first be supposed, solid ribs : they are traversed internally by 

 a spiral vessel and nerve. The membrane is double, although extremely delicate : this 

 delicacy, however r is no obstacle to the growth of appendages, such as hairs, etc., inasmuch 

 as it is frequently densely covered with them. The wing, divided by the branching and 

 anastomosing of the nervures, forms a network more or less fine. The spaces enclosed by 

 the branches are called cells or areolets; and being quite constant in form and place, they 

 are employed in the determination of groups. Three areas are particularly noticed, namely, 

 the costal, intermediate, and a?ial areas. The wing has a base, and anterior and posterior 

 margins : the first is the part attached to the sternum ; the two others define themselves. 

 The apex of the wing is the part opposite to the base. 



Various views have been expressed by different authors on the analogical relations of the 

 wings, many of which are certainly very fanciful. M. Atjdouin takes a rational common 

 sense view of these relations, and regards the wings as organs sui generis, intended for the 

 exercise of special functions. 



The legs- Each segment of the thorax supports a pair of legs. The joint which unites 

 them with the body is called the coxa or hip : it is held in its socket by a ligament. The 

 motions of the leg are controlled more or less by the form of the coxa. The thigh is the 

 largest portion of the leg : its form is various ; it is cylindrical or flattened, it is straight 

 or arched. If the insect leaps, the posterior thighs are thick and strong. The legs are also 

 more or less spinous. 



The tibia is the next part of the leg, and forms an angle with the thigh. It is more 



