VII] INTERNAL ANATOMY 6l 



cells to such an extent that their nuclei are forced to the 

 periphery. Moreover, these cells are granular in appearance, 

 in contradistinction to those of the central gland, which are 

 clear The lumen of the central gland is much smaller than 

 that of each lateral gland, and the clear secretion almost 

 entirely fills the cells. 



This central gland has long been supposed to be the source 

 of the irritating substance which is inoculated when a mosquito 

 begins to feed, and accordingly is still commonly known under 

 the name of " Poison-Gland." Schaudinn, however, has 

 shewn that its secretion produces no effect when injected into 

 the skin and the irritation following a bite is due to the entrance 

 into the wound of a fungus, which is derived from the ceso- 

 phageal diver ticula. 



(b) The reproductive organs. The genital organs of the 

 female consist of a pair of lobulated masses containing numerous 

 eggs in various stages of development. From each a short wide 

 duct leads into a common oviduct opening to the exterior in 

 the eighth segment. Into the common duct open three short 

 seminal receptacles and also a cement-gland. The function of 

 the latter is probably to secrete a protective coating for the 



eggs. 



The male genital organs consist of a pair of minute testes 

 situated in the eighth segment. From each arises a simple 

 tube, the vas deferens, and the two unite just before the 

 opening to the exterior, forming a common ejaculatory duct. 

 The latter ends in a short penis and the external aperture, 

 situated on the ninth segment, is guarded by an elaborate 

 arrangement of claspers, or gonapophyses, that are of some 

 importance from a classificatory point of view. The sper- 

 matozoa are stored, and also complete their development, in 

 two receptaculae seminales, opening one on each side into the 

 vasa deferentia immediately before their junction. 



(c) The respiratory system. This consists of two large 

 tracheae running longitudinally one on each side of the body 

 and giving off branches to all the internal organs. Each 

 main longitudinal trunk is connected by means of short branches 

 with the stigmata, or breathing pores, of which there are two 



