34 PREDACIOUS AND PARASITIC 



may sometimes be observed behind them ; but I am inclined to 

 think that it has no special function as to the hooks, but probably 

 assists in the general movements of the skin. 



As the larva extends its head by continuing its evagination, 

 folds become visible representing another segment, almost entirely 

 dorsal, which bears on either side a fleshy protuberance carrying 

 two papillae, which are no doubt organs of special sense. These 

 are shown on PI. III. at Figs. 5 and 9, and will be further des- 

 cribed. Midway between these protuberances an implication of 

 the epidermis, parallel to the length of the larvae (for at this stage 

 of extension the dorsal surface is considerably in advance of the 

 ventral) forms the upper margin of the mouth, from which the 

 points of the piercing and sucking organ may generally be seen 

 protruding. They are shown at e in Fig. 9. 



This latter organ has been figured by Reaumur, De Geer, and 

 other writers, but scarcely in sufficient detail for the figures to be 

 useful. It may and probably does represent the first two segments 

 of the head. 



In general shape it may be described as resembling the bill of 

 a flat-billed bird, such as a duck. It consists, as to its upper part 

 of an arched, chitinous framework, with posterior extensions form- 

 ing two elongated blades or plates {d, d, Fig. 2). Forwards, a 

 long spear-headed or lancet-shaped process extends to form the 

 upper half of the " bill," having its extremity slightly rounded and 

 with a central groove, somewhat like a carpenter's gouge. This is 

 opposed on the underside by a plate of somewhat similar shape, 

 but deeply indented on either side, and furnished at its extremity, 

 which is pointed obliquely, with a thin, hard edge of great trans- 

 parency (PI. III., Fig. 6). This half of the organ is not articu- 

 lated in any way, but its base is lost in the mass of muscles {e, e^ 

 Fig. 4), which, surrounding and inserted into the flat plates before 

 mentioned, give appropriate movement to the two halves of the 

 " bill." 



These latter are continuous with, and merge into, the upper 

 and lower surfaces respectively of the pharynx, which, protected by 

 the chitinous plates and strengthened by a series of slight rings of 

 this material (occasionally the rings seem to become plates), passes 

 through the muscle, as is indicated at/,/. Fig. 4, and continues 



