THOMPSON: ANATOMY OF MOSQUITO. 
181 
depressions or pits in the wall of the head. The dermis of the pala¬ 
tum remains in position. The mandibles and maxillae undergo 
almost no metamorphosis prior to pupation. Shortly before the 
moult, their dermis thickens and takes on some of the staining 
reactions of the dermis of an imaginal bud, assuming a condition 
intermediate between the cells of the llabellal dermis and the cells 
of the labral, labial, or palp buds. 
The larvae of Anopheles pass through a similar series of changes 
as far as their mouthparts are involved, so that the wrigglers of 
both Culex and Anopheles have at maturity an evaginate labral bud, 
invaginate buds for the labium and the maxillary joalpi, thickened 
mandibular and maxillary dermis, and the dermis of the flabellae 
and epipharynx retracted from the cuticle. The changes beyond 
pupation are not known for Anopheles. With Culex, the succes¬ 
sive alterations during the pupation moult are shown in figures 48 
-50 on plate 16. As the head cuticle is sloughed, the labral bud 
swings over into the plane of the other mouthparts. Probably 
its rapid growth just prior to the moult is an important factor in 
rupturing the head cuticle, while the change of position during 
pupation must assist in pushing the head case away at an angle 
favorable to the extraction of the ventral mouthparts (pi. 15, fig. 
36). The change of position is partly due to the growth of the 
labrum, partly to a contraction of the retractors of the flabellae, and 
partly to a shortening of the dorsal wall of the buccal cavity. The 
moult reduces the retractor muscles to ovoid masses (pi. 17, fig. 56, 
retr fl), and shifts the flabellal depressions back to the entrance of 
the pharynx. The mandibles and maxillae are withdrawn as cylin¬ 
drical tubes. The bud of the maxillary palpus elongates slowly at 
first and the labial bud has a still more tardy evagination. This is 
probably to allow time for the retraction of the transverse fold 
formed by the hypodermis of the transverse line, mental sclerite, 
and the front wall of the pocket of the bud (pi. 15, figs. 34, 36, 
fold ). 
The mouthparts of the pupa are closely pressed together (pi. 
14, fig. 24) and form the central part of an ovoid shield which 
covers the front and sides of the body. The antennae, legs, wings, 
and halteres successively build the lateral parts of this shield. The 
shield is in close contact with the body along its borders posteriorly 
and ventrally, and above in front the central part is fused to the 
