THOMPSON : ANATOMY OF MOSQUITO. 
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connects this ganglion with the supra-esophageal ganglion. The 
overlying cuticle is not modified (pi. 12, fig. 2 ; pi. 13, fig. 8, oc). 
These ocelli are not present in the larva, but develop during the 
pupation moult. Probably they represent in a vestigial form the 
lateral members of the three ocelli found on the head of many 
Nematocerous flies. If this is the case, no trace of the median 
member can be found. 
During the pupal stage the nervous system undergoes gradual 
changes which are growth rather than a metamorphosis, increasing 
greatly in size and probably also in complexity. The brain of the 
imago is relatively enormous and there are two huge optic ganglia 
united above to the supra-esophageal ganglion (pi. 13, fig. 9-11, 
o gang ). A small buccal ganglion lies above the pharynx, between 
the last pair of elevators of the palate and the valvular muscles. 
The larva, on the other hand, has a small, transverse supra-esophageal 
ganglion and an insignificant infra-esophageal ganglion (pi. 15, figs. 
29, 30). The swollen lateral apices of the sujwa-esophageal mass 
correspond to the optic ganglia of the imagp (o gang). The buccal 
ganglion is very small (pi. 15, fig. 32, b gang). The thoracic ganglia 
of the imago are united to form a single elongate mass. In the 
abdomen six ganglia are distinct and occupy the joints from the 
second to the seventh inclusive. In the larvae, however, (pi. 14, 
fig. 26) there are three separate thoracic ganglia and the first eight 
abdominal joints are furnished with a ganglion apiece. During the 
later larval instars, the ganglia of the first and eighth joints of the 
abdomen shift to the anterior borders of their respective segments, 
and before pupation occurs, the ganglion of the first joint enters the 
thorax (pi. 17, fig. 54). Later, it fuses with the thoracic ganglia 
to form the thoracic ganglion mass. Some hours after pupation, the 
ganglion of the eighth abdominal segment passes into the seventh 
joint (pi. 17, fig. 55) and ultimately fuses with the ganglion already 
present in the segment to form the sixth abdominal ganglion of the 
imago. 
The imaginal buds share in the simplicity of the metamorphosis. 
With the exception of those for the antennae, none are deeply 
invaginated, and as far as the mandibles, maxillae, and the tail fans 
of the pupa are concerned, the formative dermis does not alter 
beyond the thickening which is the invariable preliminary to the 
formation of an imaginal bud. The labium, maxillary palpi, tho- 
