ENEMIES OF APHIDES. 175 



portion of the rostrum corresponds. In Figs. 5, 6, 7, 8, and 9, 

 the rostrum is shown in detail. It consists, as to its main struc- 

 ture, of two elongated fleshy lobes in four segments, which are 

 closely united on the underside (assuming the rostrum to be 

 extended); but on the upper surface form a deep groove, within 

 which are the delicate setse which constitute the piercing organ. 

 The rostrum takes its rise in, or rather is a prolongation of, the 

 front portion of the head, which is hollowed out on the underside 

 so as to receive the organ when in repose, and folded back beneath 

 the thorax. 



When the rostrum is extended, the cavity thus formed is 

 covered by a membrane, no doubt of a muscular nature, which at 

 such times becomes tense and rigid, and which is continuous with 

 the skin of the rostrum. The extremities of the labial lobes, as 

 showii at Fig. 9, are two small, cushion-like organs, bearing each 

 several stiff hairs, and which are all that represent the extensive 

 labial terminations of the Diptera. Within the groove terminated 

 by these cushions lie the four setse constituting the alimentary 

 apparatus. They consist of fine chitinous blades, the two central 

 ones being nearly flat, parallel-sided lancets of great length, and 

 much resembling in form the blade of a narrow sword. Each of 

 these is grooved on the opposing faces, and the two sections 

 pointed at the extremity and working one against the other form 

 not only the weapon by which the prey is struck, but the passage 

 by which the ingestion of the victim's juices is accomplished. 

 The sharp and channelled extremities of these piercing setse are 

 shown at Fig. 7, and observation has satisfied me that in action 

 they operate by a sliding action one upon the other, this being 

 probably given by the alternate compression and dilation of the 

 spiral muscular bundles enveloping the pharynx, as seen in Fig. 

 10. The two remaining setse are thin and hollowed throughout 

 so as to form sheaths, which, closing in on either side, protect the 

 lancet setse throughout their entire length. These sheaths are 

 shown in Fig. 6 in their natural position, and the extremity of one 

 from an allied genus is more highly magnified at Fig. 8. Towards 

 the extremity they are more or less serrated, or sometimes provided 

 with knobby protuberances, and the thin edges, which frequently 

 overlap, are ribbed and notched in a definite pattern, in order, 



