TRANSMISSION. 665 



another mammal it flies to a suitable pond or other 

 collection of water, where it deposits its eggs. 



"The adult mosquito lays its eggs on the surface Development. 

 of the water. The eggs float on the water for 

 some days (two to four), after which they hatch 

 and permit the escape of the larva. 



"The larva is a free-swimming, worm-like ani- 

 mal, which eats greedily and grows rapidly, cast- 

 ing its skin several times in the process, till it 

 reaches its full development. At this stage it sud- 

 denly changes its form ; casting its skin, the worm- 

 like larva assumes a comma shape and so becomes 

 the pupa or nympha. 



"During the pupal period the insect ceases to 

 eat; profound anatomical changes take place with- 

 in the pupal skin, whereby the masticatory mouth- 

 parts of the larva are converted into the suctorial 

 apparatus of the adult insect or imago. After a 

 certain number of days the pupa case ruptures and 

 the adult insect is liberated, furnished with wings 

 and legs adapted for a life in the air." (James 

 and Listen.) 



In one instance Howard found the life cycle of 

 Anopheles maculipennis to be: "Egg stage, three 

 days; larval stage, sixteen days; pupal stage, five 

 days, making a total period in the early stages of 

 twenty-four days." The rapidity with which this 

 process takes place depends largely on the tem- 

 perature; it is more rapid in the hot weather of 

 July and August than in the cold days of May. 

 Anopheles usually does not lay its eggs in tin cans 

 or barrels of water, but preferably in more open 

 or cleaner water. Excavations which have become 

 filled with water are favorable places, as are also 

 collections of water from springs. 



