CONDITIONS AFFECTING EGGS 281 



BREEDING HABITS. 

 THE EGGS. 



The different stages of this mosqinto are carefully described in the systematic 

 portion of this work. The eggs, as above described, are frequently laid in small, 

 irregular groups some distance above the margin of the water, and may remain 

 dry for long periods, hatching when reached by the water. They develop better 

 after having been dry for a period. Reed and Carroll state : 



" The resistance of stegomyia's eggs to external influences is worthy of note. 

 Drying seems to be but little injurious to their subsequent fertility. We have 

 found that eggs dried on filter paper, and kept for periods of from ten to ninety 

 days, will promptly hatch when again submerged in water. Dried eggs brought 

 with us from Havana, in February, were easily hatched during the month of 

 May, in Washington, furnished about 60 per cent, of the usual number of larvae 

 hatched from fresh eggs. Freezing does not destroy the fertility of the eggs. 

 Although freezing with a mixture of salt and ice for thirty minutes has several 

 times seemed to prevent subsequent hatching; on one occasion a batch of one 

 hundred and fifty-five eggs, freshly deposited, which were frozen at a tempera- 

 ture of -17° C, for one hour, then thawed out at room temperature and placed in 

 the incubator at 35° C, began to hatch on the sixth day, the majority furnishing 

 active larv^ on the eighth day. In another observation, freshly deposited eggs, 

 frozen at -17° C. for half an hour on two successive days, began to hatch on the 

 third day as usual at incubator temperature. The resistance of stegomyia's 

 eggs to drying for a period of three months would appear to demonstrate that 

 this genus of mosquito could survive the winter in Havana, without the presence 

 of hibernating females. Doubtless the genus is preserved in both ways. It is 

 probable that the same could occur in our extreme southern latitudes." 



The Brazilian investigators at Rio de Janeiro determined that the eggs will, 

 when dry, preserve their vitality unimpaired for five months. Eggs placed on 

 filter paper and kept in test-tubes developed after this period but beyond that 

 period they failed to hatch. Francis asserts that eggs hatched which he had 

 kept dry during six and a half months. Eggs sent to Theobald in England, 

 from Cuba, hatched after two months and a half. It is to be supposed that under 

 natural conditions the eggs of calopus will survive out of water even longer than 

 the longest period achieved experimentally. It should be remembered that in the 

 majority of the species of Aides the eggs do not hatch until the following year 

 and that a percentage, with some, and we believe with many species, remains 

 dormant until a second year. 



Agramonte (a member of the American commission to Cuba), in a chapter on 

 mosquitoes and yellow fever appended to Berkeley's "Laboratory Work with 

 Mosquitoes " (New York, 1903), states that the duration of the egg-state varies 

 according to the season of the year, the temperature of the water and the 

 chemical conditions of the water. He shows that with the lye of wood-ashes, em- 

 ployed by laundresses in Cuba for the purpose of whitening the clothes, the eggs 

 hatch more quickly than in the dirty water of overflows and gutters, and yet the 

 latter contains more organic matter. 



The duration of the egg-stage according to Agramonte is from fifteen hours 

 to three days. J. R. Taylor, of Las Animas Hospital, Havana, gives the dura- 

 tion of the egg-stage as 12 to 24 hours. The first American commission to Vera 



