130 PROC. ENT. SOC. WASH., VOL. 23, NO. 6, JUNE, 1921 



the posterior hooks of such primary larvae as that of Compsilura concinnata 

 Meig. 



In this stage the larva is metapneustic; the posterior stigmata open a little 

 to the dorsal side of the apex of the last segment; each stigma presents two 

 respiratory papillae; the "felt-chambers" (Fig. 2) are about 6.5 as long as their 

 diameter. 



The mouth-hook or bucco-pharyngeal armature is represented by the Figures 

 3, 4 and 5 and it is therefore unnecessary to describe it in detail. In this stage 

 it is without articulations; the median tooth presents 5 or 6 minute denticles 

 (Fig. 5) on the cutting edge. In the newly hatched larva the armature has the 

 form represented in the Figure 3, but at the end of this stage its aspect is super- 

 ficially very different owing to a progressive chitinization which takes place in 

 the pharyngeal cuticula surrounding the basal plates, and especially the dorsal 

 wing (Fig. 4). This increase in the area of the basal portion of the armature 

 corresponds to an increase during the first stage of the posterior part of the 

 pharynx containing the elevator muscles and is doubtless due to the excitation 

 of the pharyngeal epithelium by these muscles. 



The sensorial organs of the larva are minute. The cephalic organs consist 

 chiefly of a dorsal element, plano-convex in outline the antenna and a more 

 ventral group of minute organs, constituting the maxilla. The sensorial organs 

 of the body segments comprise a certain number of minute clavate hairs and 

 more numerous minute circular pits. These organs are constant in number and 

 distribution (Fig. 2). 



The second stage larva (Fig. 6) measures about 4.0 mm. x 1.0 mm. (hiber- 

 nating larvae). The larva is now more robust than in the first stage. The 

 cuticula is colorless and transparent but the spine armature is relatively some- 

 what more conspicuous than in the first stage. On the first three segments 

 there exists only an anterior band of spines which on segment II and III is 

 broadened so as to form an oval plate in the ventral region. On segment IV 

 a posterior band appears in the ventral region. On segment V a few curving 

 rows of spines appear at the pleural extremity of this ventral band. The dorsal 

 anterior band of segment VI is broken in the pleural region, and the pleural 

 group above the posterior ventral band is larger. On segment VII the dorsal 

 anterior band is feebly developed; the anterior pleural group is divided: and the 

 anterior ventral band consists of only a few rows of small spines. On the 

 posterior border a single short dorsal row appears. On segment VIII the dorsal 

 anterior band is very feebly developed; there is a pleural group semi-circular in 

 form, opposite the pleural group on the posterior border of segment VII; and 

 the ventral anterior band is feeble and medially interrupted. On this segment 

 the posterior band is now almost complete though still rather feeble in the 

 dorsal region. On segment IX the dorsal part of the anterior band is absent 

 and the pleural and ventral anterior groups are feeble*; a continuous, moderately 

 broad band of heavy spines exists on the posterior border. On segment X the 

 anterior band is represented only by a few minute pleural spines and a single 

 ventral row. The posterior band is like that on the preceding segment. On 

 the last segment there exists a pleural group of curving rows of feeble spines, a 

 median ventral group and dorsal and ventral groups of stigmatic spines as in 

 the first stage. 



