24 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I39 



strongly developed jaws (fig. 5 B,C), the toothed lobes of which come 

 together or overlap for grasping and biting. Yet these larvae have 

 labral brushes and some of the other special features of particle-feed- 

 ing larvae, so it is difficult to say whether they represent a partway 

 stage in the evolution of filter feeding, or have been secondarily 

 adapted for feeding on whole live prey. In some species the larvae are 

 particle feeders in the first instar and become predaceous in their later 

 instars. It would appear, therefore, as said by Bates (1949), "that 

 the predacious habit has developed independently in the larvae of a 

 number of mosquito groups, involving distinct adaptations both of 

 structure and behavior." 



THE THORAX 



The larval thorax has a simple oval form, in which the interseg- 

 mental lines are but faintly marked as grooves of the cuticle, and 

 there is no external trace of appendages. In the fourth instar the 

 thorax becomes conspicuously enlarged (fig. 9 A). Beneath the cuticle 

 on the ventral side are now plainly visible the extroverted wings and 

 legs of the future pupa, and on the dorsal side the pupal respiratory 

 trumpets. On removal of the cuticle (C) the legs are seen to be long, 

 fully segmented appendages (E) closely folded in loops against the 

 sides of the thorax. The forewings (W 2 ) are large pads corrugated 

 in their basal parts (D) to allow expansion; the smaller hindwings 

 (W 3 ) are more slender and tapering free folds of the metanotum. It 

 has been shown by Imms (1908) that the rudiments of the wings, 

 legs, and respiratory trumpets are formed in a young larval instar of 

 Anopheles as integumental folds in pockets of the epidermis (B). Ap- 

 parently they are extruded beneath the cuticle at the beginning of the 

 fourth instar. This early eversion of the wings and legs occurs also 

 in other nematocerous larvae, such as Diva, Corethra, and Chirono- 

 mus, shown by Miall and Hammond (1900) in Chironomus. 



On each anterior lateral angle of the thoracic dorsum of Anopheles 

 larvae there is usually to be seen a pair of minute, tapering, trans- 

 parent lobes arising from a common base (fig. 9 A, no). These struc- 

 tures are known as the "notched organs." They are retractile and 

 hence are not visible on all specimens, or only their tips may project. 

 Between the lobes of each pair is a funnel-shaped depression that ends 

 in a strand, which is said by Chang and Richart (1951) to be at- 

 tached to the neighboring dorsal tracheal trunk. These writers con- 

 tend, therefore, that the organs are the "prepupal respiratory trum- 

 pets." However, when the cuticle of a fourth-instar larva is removed, 



