C ULICIDM 



783 



7-10. Hind-Gut. — This runs from the end of the mid-gut to the anus, being 

 divided into the following regions : — 



(1) A dorsally bent portion, the ileum, lined by flattened epithelium. 



(2) A ventrally bent portion, the colon, lined by cubical epithelium. 



(3) A dilated portion, the rectum, which has six large ovoid papillae. 



The rectum narrows just before the anus, which opens on the last segment 

 of the body. 



. Malpighian Tubes.- — -There are five Malpighian tubes opening at the junction 

 of the mid- and hind-gut. 



Salivary Glands .—-The salivary glands consist of two groups, each con- 

 taining three acini, lying on each side of the body, in the anterior portion of 

 the thorax, close against the prosternum, and extending almost as far back 

 as the proventriculus. The ducts from each 

 of these acini unite together to form a 

 single duct on each side, which passes for- 

 wards through the neck into the head, where 

 it unites beneath the suboesophageal ganglion, 

 with its fellow of the opposite side, to form 

 a common salivary duct. This duct passes 

 forwards to end in the salivary pump, which 

 is continuous with the salivary groove or 

 canal of the hypopharynx. The duct of the 

 salivary gland, therefore, is not in any way 

 connected with the alimentary canal. These 

 glands, which are much larger in the female 

 than in the male, are composed of acini, 

 surrounded by a basement membrane which 

 is very delicate and structureless, and upon 

 which rests a single layer of epithelial cells 

 surrounding a central lumen. The whole 

 acinus lies in a cleft in the fat-body. 



Space does not permit of descriptions of the 

 vascular, nervous, and muscular systems being 

 included. 



Reproductive Organs.- — -The female repro- 

 ductive organs consist of ovaries, oviducts, and a common oviduct, a mucous 

 gland and its duct, and a spermatheca and duct ; while the male organs are 

 testes and vasa deferentia, which, after receiving the ducts of the receptacula 

 seminis, run to an ejaculatory duct, v/hich ends in a short penis. 



Life-History. — A mosquito passes through a complicated Hfe 

 cycle, consisting of an egg, a larval, and a pupal stage, the last- 

 named giving rise to the perfect insect or imago. 



Soon after a female insect is hatched it probably becomes fertilized, 

 though some authorities believe that this does not take place until 

 after the first meal of blood, which in any case precedes the ovi- 

 position, which takes place in the early morning. 



The eggs, which number about one hundred, are laid upon the 

 surface of the water, on v/hich they may be seen arranged in stars, 

 rows, or triangles. 



The eggs of A. maculipennis are boat-shaped, about 0-5 to i 

 millimetre in length, with a fiat upper and convex lower surface, 

 and with one end somewhat broader than the other. The head of 

 the larva will be found at this broader anterior end. The upper 

 surface is granular and reticulated, while the lower is smooth. 

 On each side of the middle third the chitinous capsule is thrown into 

 folds, called floats, while the margin projects as a chitinous frill, 



Fig. 387.^ — -Egg of Anopheles 

 maculipennis. 



(After Nuttall and Shipley.) 



On the left the egg is seen 

 from above, and on the right 

 from the side. 



