268 AYERS ON THE DEVELOPMENT 



conception of its form than any brief description would serve to do. In this stage the 



cuticula extends over the larva as an unbroken sheet, except at the mouth opening ; here 



it is wanting in a circular area, the external opening of the stomodaeum. It projects 



forward from the forehead to form a sheath for the antennae, at the bases of which it is 



thin and flexible, allowing slight movements of the organ. (PI. 25, fig. 19.) Below the 



^4^^^ antennae on the ventral surface the mandibles are 



X. (\^^^ : :ssa ^4^C = ^ „ formed as scythe-shaped, pointed, tubular projections 



| ''^^^Ss^^ff^^^^ye of the cuticula. which grows gradually thicker 



V/Vjs ^^^^^S^^ 5=s "^-\ an d yellowish toward the tips, where it shows the 



1 ^ 7^^^SS^ s^-=ySg^\ characteristic color of chitin. Here, also, as in the 



/\ if ^*^^$?i*yi antennae, the cuticula thins out at the base of the 



I \A ^*^ organs, allowing great freedom of motion to the man- 



(l ^^ dibles. Below these the cuticula is thrown into a 



\\ double-layered fold which varies in its structure with 



The mandible and antSarf the left side of the body the degree of development of the lar va. For succes- 



of the larva figured in pi. 24, fig. 20. The surfaces of sive Stages of this fold, Ol" Under lip, See pi. 24, figS. 

 the mandibular muscles are shown. X about 500. -. ,- -. „ orv m m k -it i r. .i 



17, 19, 20, 21, 24. As will be seen from these 

 figures, the lip is at first a simple projection, later becoming bent up at the tip. Some- 

 times it presents lateral grooves for the reception of the tip of the mandibles, thereby 

 increasing their efficiency in cutting the yolk mass of the host into bits suitable for swal- 

 lowing. The lip sometimes strongly resembles the lower mandible of a hawk or an owl. 

 It may be bifid but its upper surface is always concave. One larva was found in which 

 the mouth was kidney-shaped and the lip proper extended as a gutter from a point on 

 each side of this opening downwards, and outwards, the edges gradually converging in an 

 up-turned, sharply pointed tip. This fold was only a part of a larger lip-fold extending to, 

 and losing itself in, the lateral boundaries of the body w a ll posterior to the lip proper. 

 Beneath this was a broad fold which united with the body midway between the primary 

 and the secondary lips. This fold seemed to function as a support to the lip as well as a 

 scoop to aid the larva in feeding. There is a pair of cuticular structures of a problemat- 

 ical nature, usually one on each side of the body between the mandibles and the 

 lower lip, but varying considerably in their relative positions indifferent larvae. (Com- 

 pare pi. 24, figs. 17, 19, 20 ; pi. 25, figs, land 6.) They vary greatly in structure but each 

 usually consists of a cup-like depression in the cuticle in which there are secondary 

 cup-like depressions. The cup may be rendered imperfect by the extension into its area 

 of a narrow band of the smooth cuticula. The secondary cups may present a simple out- 

 line or may be irregular in shape and separated from each other by a band-like margin. 

 These structures assume a more lateral position as the nervous system increases in its devel- 

 opment, and as they lie at all times on either side of the suboesophageal ganglion they may 

 function as sense organs. No direct connection between these structures and the 

 nervous cord could be traced. Posterior to the structures just described there is a thick- 

 ened fold of the cuticula most prominent in the median dorsal line, which gradually lessens 

 until it finally disappears in the lateral walls of the body. This fold forms a boundary line 

 between two distinct regions of the body, the cephalic and the abdominal. It serves 

 to strengthen the cuticular walls of the cephalic region, and like all other cuticular 



