The characteristic position of anopheles. 



in the same straight line. On the other hand, the abdomen and 

 thorax of a " culex " always form an angle with the head and proboscis, 

 so that these mosquitoes appear " hunch-backed." 



SOME CHARACTERISTICS OF THE LARV^ AND EGGS NOT DESCRIBED IN 



THE PRECEDING PAGES. 



1. The food of anopheles larvce. This consists chiefly of 

 minute water animals, which abound among algae and other water 

 plants. Larvae cannot subsist upon a vegetable diet alone, and the 

 duration of the larval stage depends chiefly upon the supply of 

 animal food. When this is small in proportion to the number of 

 larvae, the stronger larvse kill and eat the weaker. 



2. The duration of the egg stage and the resistance of ova to 

 drying. When anopheles eggs are laid on water, they almost in- 

 variably hatch out into larvae in 48 hours. When they are laid, as 

 they frequently are, upon damp mud, the development of the 

 embryo goes on inside the egg, and when water is added to the mud 

 the larvae hatch out immediately. This observation, which was first 

 made by Captain Liston at Ellichpur in the Berars, has lately been 

 confirmed by Dr. Christophers at Mian Mir. The latter observer 

 found that, after the water in an irrigation canal or pool had been 

 emptied out, " anopheles " still laid their eggs on the soft mud, and if 

 water was again allowed to enter the canal or pool before the mud 

 had become completely dry, numerous young larvae would almost 

 immediately be found in it. It is not difficult to detect eggs which 

 are laid on the edges of pools in this way. Dr. Christophers col- 

 lected a number from pools of different degrees of dryness and 

 placed them on water with the following results. 



Number of ova Number of larvae Additional number 



Character of mud. , , , , , , . n K 



taken. hatched in 15 minutes, eventually hatched. 



Quite soft ... 12 12 



Cracked but moist ... 10 2 8 



Quite dry ... 25 5 1 

 Slab of soft mud with 



ova ; dried 12 hours. A large number 

 in the sun 



It will be seen, therefore, that pools which are, to all intents and 

 purposes, quite dry, may contain numerous larvae almost immediately 

 after a shower of rain. 



[57 



