60 CULICIDiE [CH. 



by thin chitinous lamellae and therefore serves the purpose of 

 a duct. At the base of the hypopharynx is the salivary 

 receptacle or pump, connecting the salivary groove with the 

 common salivary duct. The pump is somewhat drum-hke in 

 form, its membrane being moved by muscles by means of 

 which the saliva is first pumped out of the glands and then 

 down the salivary groove to the tip of the hypopharynx. The 

 salivary pump is situated beneath the floor of the buccal cavity. 

 From its posterior end a median, common salivary duct extends 

 backwards until it reaches the commencement of the pharynx, 

 at which point it branches into two. These secondary ducts 

 run side by side along the ventral wall of the neck into the 

 thoracic cavity, where they diverge and each branches into 

 three smaller ducts. Each of the latter terminates in a salivary 

 gland, there being three glands on each side. 



These three salivary glands are at first arranged in the form 

 of a triangle but subsequently their position changes and the 

 gland which at first occupies a dorsal position comes to lie in 

 between the other two glands. It is usually known as the 

 " central gland " and differs both in size and structure from 

 the other two, known as the " lateral glands." 



The size of the glands varies according to the size of the 

 insect but is always greater in the females than in the males. 

 The dimensions of the glands of an average-sized female are 

 as follows : length of lateral glands, 880 /u. ; length of central 

 gland, 510 /u; width of glands, 85 /li. In the male the large 

 glands only measure about 200 /a in length by 50 /u. in breadth. 



The salivary glands are of very great importance from a 

 parasitological point of view, since the infective sporozoites 

 of malaria congregate within the cells of these organs and are 

 passed out with the salivary secretion. Therefore by a micro- 

 scopical examination of these glands it is possible to find out 

 whether or not a mosquito is infected. 



The structure of the three glands is similar, each consisting 

 of an elongated sac the lumen of which is surrounded by a single 

 layer of secretory cells, but they differ somewhat in their finer 

 details. The acinus of each of the lateral glands is more or less 

 filled with an abundant secretion, which also fills the secretory 



