48 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 1 39 



the larva degenerate and each is replaced by three slender tubules 

 generated from cells in the neck of the larval gland. 



The central nervous system undergoes little change in the pupa 

 other than growth and union of some of the ganglia. The first ab- 

 dominal ganglion of the larva is drawn into the thorax, where it 

 fuses with the metathoracic ganglion, and later the four ganglia now in 

 the thorax condense into a single mass. The last abdominal ganglion 

 of the larva unites with the ganglion of the seventh segment. In the 

 adult mosquito, therefore, there are only six separate ganglia in the 

 abdomen (fig. 30 C). In the head, as described by Woolley (1943) 

 for Aedes, the brain and the optic lobes grow rapidly by peripheral 

 formation of new cells. The circumoesophageal connectives shorten 

 and the suboesophageal ganglion unites with the brain around the 

 oesophagus. 



Though the visible changes that take place in the nervous system 

 are slight, there must be a considerable reorganization of the internal 

 structure. The behavior and instincts of the adult mosquito are en- 

 tirely different from those of the larva. Since the activities of the in- 

 sect resulting from sensory stimuli are determined by established 

 neuromuscular pathways and synapses in the central nervous system, 

 the system that serves the larva must be entirely reorganized into one 

 appropriate for the activities of the adult. Of this, however, we know 

 little or nothing in any insect. 



III. THE ADULT 



The adult mosquito fully formed within the pupa has now only to 

 cast off its pupal mold to gain its freedom in the garb of a mature 

 winged insect. But this is not easily done since the confined mosquito 

 has no instruments for cutting or breaking the pupal cuticle. More- 

 over, the wings, legs, antennae, and mouth parts are enclosed in tight- 

 fitting sheaths, from which they must be slowly extracted. However, 

 much as we might wish that the mosquito should remain a prisoner in 

 the pupal skin, nature has made provision for its liberation. 



As noted by several observers, the first evidence that the adult is 

 about to emerge is the appearance of a film of air beneath the pupal 

 cuticle on the back of the thorax. A slight retraction of the adult ap- 

 parently breaks the connections of the pupal trumpets with the tracheal 

 system and thus allows air to escape beneath the cuticle. Usually a 

 short piece of trachea remains attached to the base of each trumpet. 

 According to Marshall and Staley (1932) rhythmical movements now 

 begin in the sucking pump of the adult which draw the air forward, 



