400 PREDACIOUS AND PARASITIC 



under any higher magnifying power than that of an ordinary hand- 

 glass. On PL XIX., at Fig. i, I have reproduced Mr. Bower- 

 bank's excellent drawings showing by means of arrows the course 

 taken by the currents within the veins. So far as I have been able 

 to observe, it appears that the veins themselves form the circu- 

 latory channels or vessels, the fine tracheae which pass through 

 them being perpetually bathed in the moving fluid. 



An enlargement of portions of the wing veins is given at Figs. 

 2, 3, and 4 on the same Plate, showing within^ the trachea easily 

 visible from its characteristic structure. These tracheal tubes may 

 be easily seen and their course traced throughout the principal 

 veins of the wing by placing it in Canada balsam (fairly thin) 

 under a cover-glass, when, on exerting a slight pressure by means 

 of a needle while the slide rests upon the stage, the balsam may 

 be seen following up the tracheae and driving the air before it in a 

 very striking manner. The diameter of the tracheal passages, as 

 shown in Fig. 4, is stated by Mr. Bowerbank at about 1/2 2 2 2nd of 

 an inch, while the circulating passages within which they lie are 

 about i/4o8th of an inch. 



The Antenna of the Imago. 



The antennae of the Heinerobiiiice have shared the confusion 

 which has affected the descriptions of the family. They have 

 been variously described as moniliform, fiUform, setiform, beaded, 

 cylindrical, and thread-like. 



The antennae of HemerobiidcE are always of the monili- 

 form or beaded type, although the shape of the segments 

 varies from that of a shortened and reversed champagne bottle 

 to almost globular. The number of segments is always con- 

 siderable, fifty to sixty being about the general number. The 

 lower segments sometimes present a slight elongation, but 

 the ultimate segment differs in no respect from those pre- 

 ceding it, except that it is terminal. The antennae are more 

 or less hirsute, and some species — as that figured on Plate 

 XIX., Fig. 8 — are characterised by short, stiff bristles, arranged 

 almost or quite at right angles to the axis of the antennae, on the 

 edge of each segment. 



The antennae of the Chrysopidce. are long, consisting of some 



