NO. 8 ANATOMICAL LIFE OF THE MOSQUITO SNODGRASS 63 



inner end of the organ opens through the mouth (Mth) into the 

 narrow first part of the alimentary canal, and at each side of the mouth 

 projects a small process (y) on which are attached two antagonistic 

 muscles (A, ij, 14), as in the cockroach. All these features so 

 closely duplicate those of the cibarium in the cockroach as to leave 

 no doubt that the preoral sucking pump of the mosquito is the ciba- 

 rium. In the mosquito, however, the organ has been made into a much 

 more efficient sucking apparatus than that of the cockroach by the 

 union of the edges of its lower hypopharyngeal wall with the epi- 

 pharyngeal wall, thereby converting the lumen into a closed cavity. 

 The clypeal muscles on contraction lift the flexible dorsal wall and 

 expand the lumen, drawing in the liquid food from the canal of the 

 labrum. On relaxation of the muscles the dorsal wall snaps back by 

 its own elasticity and drives the liquid from the pump back through 

 the mouth. 



On the epipharyngeal wall of the cibarial pump are small spines 

 and papillae of various kinds, some of which are sense organs. A com- 

 parative study of these structures and an armature of ventral teeth at 

 the mouth entrance has been made by Sinton and Covell (1927), and 

 Chwatt and Major (1945) in the anophelines, and by Barraud and 

 Covell (1928) in anopheline and culicine species. The epipharyngeal 

 sense organs are described by Day (1954). 



The pharyngeal pump. — From the mouth at the inner end of the 

 cibarial pump the stomodaeal section of the alimentary canal begins 

 as a narrow tube (fig. 24 A,E) that curves upward and backward in 

 the head, going between the brain (A, Br) and the suboesophageal 

 ganglion (SoeG). Behind the brain it expands into a large, bulblike 

 structure, which is the pharyngeal pump (PhP). The walls of the 

 organ when relaxed are deeply concave above and on each side, as seen 

 in cross section at B. Into the concavity of the dorsal wall is inserted 

 a pair of large muscles (A,B,E, 8) from the dorsal wall of the head 

 behind the brain, and into each lateral concavity a large flat muscle 

 (11) from the side of the cranium. Contraction of the muscles dilates 

 the lumen of the pump ; on their relaxation the walls spring together 

 again by their own elasticity. From the rear end of the pump, the 

 narrow oesophagus (Oe) proceeds through the neck into the thorax. 

 A cibarial and a pharyngeal pump like those of the mosquito are 

 common to bloodsucking nematocerous flies. Presumably the two 

 pumps work in alternate phases to keep the ingested blood flowing 

 freely back into the stomach. In the nectar-feeding male mosquito 

 the sucking apparatus is less strongly developed than in the female. 



