708 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. XXVI 



Arculus and triangle. — The radius and the media tend from the firsl' 

 to unite at the base, and in the adult wing appear to form a single veii 

 as far as the arculus. But even in the adult wing this vein may be 

 seen, as pointed out by Brogniart, to be composed of two, whose unior 

 he aptly compared to that of the barrels of a gun. Media suddenh!; 

 bends away from the radius and is met by a cross vein from the cubi; 

 tus, and thus the arculus is formed. A similar deflection of the cul)ita 

 trachete just beyond the arculus makes a place for the development oji 

 the triangle, which is completed hy two cross veins approximated upoi 

 vein J\f^. Thus only the upper end of the arculus and the inner sid( 

 of the triangle are formed from principal veins. 



Fig. 3.— Venation of the imago of Gotuiihitt; dc^criptus. 



Tracheji? and cuticular thickenings thus combine to produce a m\u[\u 

 insect wing, whose chief peculiarities arise from three transversa 

 unions of its veins, at stigma, nodus, and arculus, respectively. Adde( 

 to the usual thickening of veins and corrugation of membrane at th( 

 front border, those three unions make the part of the wing whicl 

 cuts the air and supports other parts very strong. It will be observec 

 that at the stigma })ut two or three veins are thus conjoined, at th( 

 nodus, more, and at the arculus (by means of parts accessory to th( 

 arculus) all the principal veins are bound together across the basa 

 part of the wing. A line drawn from the outer end of the stigmi 

 to the hind angle of the triangle divides the wing into two ai^as 

 the anterior of which includes the strong framework of the wing 

 whd.^ the other is yielding membrane with weak venation, adapting th( 

 wing for that rapid sculling action in air by which forward motion i.- 

 produced. 



