174 PREDACIOUS AND PARASITIC 



slight pressure or friction suffices to detach these curious appur- 

 tenances. I have been inclined to imagine that they were hollow 

 tubes, which, originally cylindrical, as appears from the form of 

 the base, had collapsed, from the delicacy of the membrane of 

 which they were found ; but an extended observation scarcely 

 supports this view. Bristles of a similar form and structure are 

 sparsely scattered on the general surface of the abdomen, thorax, 

 and head, and one or two are generally found on the femora and 

 a few on the first joints of the antennae. Hairs and bristles of 

 ordinary tapering form are intermixed, the proportion increasing 

 on the femora and thicker joints of antennae, whilst finer hairs are 

 alone found on the tibiae and terminal antennal joints. 



The head in the larva has a much more pointed form than in 

 the nymph or imago, the apex being formed by the base of the 

 rostrum and the rather long-pointed labrum, which is folded down 

 closely upon it. The antennse exhibit but little difference in the 

 size of the joints, the characteristic development of the two first 

 belonging more especially to the nymphal stage. The quasi-caudal 

 appendage, on the other hand, is remarkably prominent in the 

 larva, and has the form of a short, truncated cone, which is often 

 marked with longitudinal stripes on either side. 



The Nymph. 

 The second (or possibly the third) casting of the larval skin 

 reveals the wing-pads which indicate the nymph, and at this stage 

 the abdomen assumes its fuller flask-shaped form, and the thorax 

 becomes wider and shaped in a more suitable way for the support 

 of the wings. The first and esjjecially the second joints of the 

 antennae are more bulky, and the latter exhibits a marked increase 

 of size towards its anterior extremity. The rostrum, however, is 

 but little different from that of the larva. The details of this 

 organ are shown on Plate VIII., Figs. 2 and 3, representing the 

 upper and under side of the head, with the organ folded down 

 upon the ventral surface of the thorax, as when at rest. The pro- 

 tuberance of the labrum and the numerous flattened bristles are 

 noticeable features. In Fig. 4 the rostrum is shown, with the 

 piercing organ raised from the sheath, formed between the lobes 

 of the fleshy labium, for to this organ in the diptera the fleshy 



