410 



THE ANIMAL PARASITES OF MAN 



The abdomen has no limbs, is composed of eight distinct segments ; 

 the sexual and anal orifices are at the posterior end, the stigmata on the 

 sides. The intestinal canal (fig. 266) is composed of three principal divi- 

 sions ; the anterior part reaches as far as the front pair of legs, and con- 

 sists of the oesophagus, which is provided with two small lateral diver ticula. 

 [At the commencement of the oesophagus are usually three diverticula, which 

 vary in size ; they contain air, food and bacteria. F. V. T.] The mid-gut 

 reaches as far as the fifth and sixth abdominal ring ; in front it is thin, 



and has numerous small supra-oesophageal gan- 

 glia ; the posterior part is, however, more dilated. 

 Five Malpighian tubes, the excretory organs, dis- 

 charge at the place where the mid-gut passes into 

 the terminal gut. 



The pair of salivary glands have one common 

 excretory duct leading into the hypopharynx. 



The glandular body, situated in the thorax, 

 consists of three slightly serpentine tubules at 

 each side, the dorsal and ventral tubes being 

 long, the central one shorter. The above-named 

 characteristics apply to both genera Culex and 

 Anopheles. The difference consists in various 

 peculiarities in form. The genus Culex is 

 smaller, Anopheles larger. [In Anopheles the 

 ends of the ducts in the lobules are dilated, 

 whilst in most of the genera the ducts are the 

 same size all along. The lobules may bifur- 

 cate, and in Psorophora there are five lobules. 

 F. V. T.] The legs of the genus Culex are 

 about the same length as the whole body ; in 

 Anopheles they are double that length. 1 In 

 Anopheles the palpi and proboscis are of equal 

 length ; in Culex the condition is different, ac- 

 cording to sex. In the male the palpi are longer 

 than the proboscis ; in the female considerably 

 shorter and the number of joints diminished. 

 The venation of the wings exhibits further 

 points of differentiation, as also their adorn- 

 ment, though this last sign is not by any means 

 always conclusive ; most species of the genus Culex 

 have unspotted wings, whilst those of Anopheles 

 are spotted. More important is the fact that 

 in Culex the abdomen is decorated with small 

 scales, similar to those on butterflies, whereas 

 there are small bristles on the abdomen of 



Anopheles. [This cannot be said to be a character by which an 

 Anopheline may be told from a Culicine, for in such common Anopheline 

 genera as Cellia and Nyssorhynchus we get plenty of scales on the abdomen, and 



FIG. 266. Longitudinal 

 section of an Anopheles, 

 showing alimentary canal 

 (after Grassi). In the fore- 

 part of the thorax is the 

 salivary gland consisting of 

 three tubules ; ventrally, 

 the suctorial stomach ex- 

 tending into the abdominal 

 cavity ; the stomach, and 

 at the posterior end of the 

 abdomen the Malpighian 

 vessels. 



1 [This is certainly not always the case. F. V. T.] 



