DOLICHOPTJS. 135 



segments, and on each of them you see a double row of 

 white spots, which are the spiracles ; the end of the 

 abdomen bends suddenly inwards, and these last two 

 segments are called the hypopygiurn which has an outer 

 pair of appendages like fringed plates; they seem to 

 be concave and join together to protect a number of 

 internal organs of varied shape which we see projecting 

 beneath, and the use of which has been largely considered 

 by Dufour. ('Annales des Sciences Naturelles/ 3e serie, 

 tome i.) 



The wings furnish us with a good lesson, and an easy 

 one, for becoming familiar with the nerves or veins. 



The costal vein is fringed and strong, ending where the 

 prsebrachial meets it. 



The sub-costal is very short and stout. 

 The radial and cubital spring together from a dot at the 

 base of the wing, and the prcebrachial, after passing the 

 transverse vein, make a slight curve toward the cubital. 

 Now, that very slight curve is of the utmost importance, 

 both as to position and shape ; it serves to assure you of 

 this being a true Dolichopus ; it is never wanting in the 

 species never altered no, not even by a microscopic line. 

 But in one of the same family, a cousin, called Psilopus, 

 there will be a little branch at the angle of the curve, and in 

 another relation, Dolichopus diadema, the curve is rectan- 

 gular, with a little branch. This Fly is common on pools 

 overgrown with plants. 



So is Dolichopus nolilitatus, which is a gilded green fly 

 easily known by its white-tipped wings, and when examined 

 with a lens you will observe that the arista is long and very 

 hairy ; the wing very narrow, and sloping away without any 

 lobe, or even angle, the anterior lines being waved within 

 the dark patch. 



No Dolichopus ever has an axillary lobe to the wing. 

 That vein beyond the probrachial is the pobrachial ; but 

 the base of the wing offers the particular marks of the 

 group, and ought to be examined in a separated wing. I 

 dwell upon this, because the careful study of one wing is a 

 most valuable lesson : the eye learns what to look for ; it 



