208 Bucentes (Siphona) geniculata 
a deep median groove into two lateral lobes each of which bears a rudimentary 
bell-shaped antenna. 
All the segments bear black chitinous hooks with the points directed 
backward. On the cephalic and prothoracic segments are several series of 
hooks, but on the remaining segments, these are smaller and fewer in number. 
Each of the intersegmental grooves of the abdomen is margined by hooks 
whose points are oppositely directed on each side of the groove. 
The larva is metapneustic at this stage, the post-abdominal spiracles being 
terminal. These communicate with two lateral tracheal trunks. 
The mouth-parts differ considerably from those of the later stages. The 
cephalo-pharyngeal sclerite is strongly chitinised, its posterior margin being 
deeply embayed. Anteriorly it is prolonged as a slender bar and terminates 
in a wedge-shaped vertical plate which protrudes from the mouth. ’V entro- 
posteriorly to this terminal wedge, there lies a free sclerite which is probably 
homologous with the dentate sclerite of the second and third stage larvae 
(PI. XIV, fig. 10). 
The Second-stage larva is about 3 mm. long (fig. 3). All the segments 
bear small chitinous hooks, so directed that each intersegmental area is 
bounded by two sets of hooks, one set pointing backward, the other forward. 
These hooks are few in number, each segment bearing only one or two rows. 
Besides these all the segments bear several series of blunt transparent spines. 
The prothoracic spiracles (fig. 25) terminate in five or six papillae. The 
post-abdominal spiracles are borne on two tubercles, each having three clefts 
surrounded by peritremes. On the outer border of each peritreme lies a white 
spot, the opening of the perispiracular gland (figs. 18 and 19). 
The bucco-pharyngeal apparatus is similar to that of the third-stage 
larva but only half the size (fig. 11). 
Third-stage Larva. The full-grown larva, when ready to pupate, is about 
8*5 mm. long and 1-75 mm. in diameter. There are two cephalic segments, the * 
first bearing rudimentary bell-shaped antennae while the second on its ventral 
surface bears a patch of backward pointing chitinous hooks. Behind the cephalic i 
segments, eleven segments can be distinguished. Of these three are probably 
thoracic and eight abdominal. On the ventral surface these segments bear 
two series of similar hooks, one on the anterior margin pointing backwards, 
the other on the posterior margin pointing forwards. Each intersegmental 
groove is therefore bounded by two series of hooks pointing in opposite 
directions. These hooks are of two kinds—small, sharp and chitinous, and 
large, blunt and transparent. The small chitinous hooks are borne on the 
second cephalic segment and on the last three abdominal segments where they 
are directed forward (fig. 4). 
The tracheal system consists of two longitudinal trunks, united posteriorly 
by a commissure, having along their length branching lateral tracheae. 
The prothoracic spiracles, which emerge on the anterior margin of the 
first thoracic segment, are fan-shaped with from six to eight lobes. In some 
