REMARKS ON MOSQUITOES 551 



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-cesophageal ganglia ; the 

 posterior part is, however, more dilated. Four or five Malpighian tubes, the excretory 

 organs, discharge 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. 



These glandular bodies are situated in the thorax ; each consists of three slightly 

 serpentine tubules, the dorsal and ventral tubes being long, the central one shorter. 

 The above-named characteristics apply to both genera Culex and Anopheles, but in 

 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 bifurcate, 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, according to sex. In the male 

 the palpi are longer than the proboscis ; in the female considerably shorter and the 

 number of segments diminished. The venation of the wings exhibits furthur points of 

 differentiation, as also their adornment, 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 usually spotted. More important is the fact that in Culex the 



FIG. 389. Longitudinal section of an Anopheles, showing alimentary canal. In the forepart 

 of the thorax is the salivary gland consisting of three tubules ; ventrally, the suctorial stomach 

 extending into the abdominal cavity ; the stomach, and at the posterior end of the abdomen 

 the Malpighian vessels. (After Grassi.) 



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 Neocellia we get plenty of scales on the abdomen. 

 F. V. T.] An experienced observer can, however, separate the two genera by the 

 difference in size and their manner of resting. When settled they either touch the 

 resting place with all the legs or only with the four anterior legs. In consequence 

 of the different length of the legs, the body of Culexj approaches the resting place 

 more closely ; moreover, Culex holds the abdomen parallel or at an acute angle to 

 the resting surface, whereas Anopheles carries the abdomen directed upwards (at an 

 angle of about 145) and holds the head down. Both genera, however, usually only 

 rest on the four anterior legs, and then, as has long been known, Culex carries the 

 third pair directed towards the dorsurn, while those of Anopheles hang down. 



In regard to the differentiation of the species, I must refer you to the special 

 literature, and content myself by observing that about 150 species of Culex and 

 about fifty species of Anopheles have been described, of which fifty about four are 



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



