152 THE BREEDING PLACES OF STEGOMYIA 



night. Between 4 p.m. and midniglit is stated by 

 some to be tlicir most active period. For this reason 

 it is necessary to take precautions against them at 

 night as well as by day. The stegomyia is subject to 

 seasonal variations, cold being the great factor in 

 stopping biting activity and breeding. Below 75° F. 

 development is retarded, and the eggs kept at a 

 temperature of 68° F. do not hatch. It is for this 

 reason that the onset of cold weather in New Orleans 

 soon put an end to yellow fever, and that the city 

 is said to enjoy a natural immunity from December 

 to INlay. Too much stress must not be laid upon this, 

 however, as the fact remains that the mosquito readily 

 survives through the winter. The distribution and 

 history of this mosquito in towns during these months 

 require close investigation. Each female lays between 

 twenty and seventy-five eggs on the surface of the 

 water ; these are mimite, black, and cigar-shaped ; they 

 are very resistant, and have been kept in a dry state 

 for periods varying between ten and twenty days, and 

 freezing does not destroy their fertility. The eggs 

 are therefore a ready means of tiding over the cold 

 weather. Under suitable conditions of temperature 

 the eggs hatch out, according to different observers, 

 in from ten hours to three days. The result is the 

 well-known " wiggle waggle," or " wiggle tails," the 

 larval stage of the mosquito. The larvc-e are very 

 active and very sensitive, and very rapidly disappear 

 from the surface of the water in the cistern if the 

 least disturbance occurs. For this reason the water 

 barrel or vat must be approached gently if one is 



