i8o 



SOME SOUTH INDIAN" INSECTS, ETC. [CHAP. XX. 



very seriously impaired by this one disease which, it may be empha- 

 sized, is entirely carried by insects. It is not every kind of mosquito 

 that is able to carry the malarial parasites from one man to another. 

 There is now a large mass of evidence on the subject and, so far as 

 is known at present, only certain species of the Anopheline group 

 of mosquitos are implicated in the transmission ; broadly speaking, 

 they all belong to the genus Anopheles although this has been split 

 up into numerous small groups (Myzomyia, Nyssorhynchus, etc.) on 

 trivial characters which would rarely be recognised as of generic 

 importance in any other group of insects. The early stages of all 

 tin- species oi Anopheles, as in the case of other mosquitos, are 

 passed in water in which the whole life-cycle is pas- id except in 

 the adult stage. The eggs are usually deposited singly, whereas 

 in ordinary mosquitos (Culicines) they are often cemented together 

 to form little rafts which float on the surface of the water; the 

 larvae are often found in slowly-running streams and are generally 

 recognisable by their habit of resting just below and parallel with 

 the surface-film of the water, whilst on the contrary ("ulicine larvae 

 usually hang down at a considerable angle with the water-surface. 



I \< .. 78. Resting attitude oi im iph< iim 

 Mosquito, it Original.) 



Fig, 79. Resting attitud 

 Culicine Mosquito. (( triginal.) 



Both types are air-breathers and usually obtain their air-supply by 

 thrusting their delicate breathing tubes through the water-film into 

 the atmosphere; hence the applicability of oiling the surfaces of 

 infected accumulations of water, as the oil spreads out over the 

 surface as a thin film and clogs the breathing tubes of the larvae 

 and so suffocates them, The adult Anopheline mosquitos are 



