90 



in a marked degree variations in the time of hatching-. Eggs of Ste- 

 gomyia fasdata, Conchyliates musicus, Pswophora ciliata, and P. 

 howardii have been influenced to the extent of months in the time of 

 hatching by one or other of the above conditions. This point should 

 not be lost sight of in devising plans for the extermination of mos- 

 quitoes, and emphasizes the possible variability of life cycles under 

 such conditions. 



Fourth. That the hatching of eggs of many species is in some way 

 associated with agitation. In ponds that dried up and remained so 

 for months very small larvae of Conchyliates, Psorophora, and a few 

 species of Culex could be found in a few hours after sufficient rain 

 fell to produce currents and a shifting of the eggs. In the laboratory 

 eggs were hatched by agitation, while members of the same batch left 

 undisturbed remained unhatched for months. Seasons of occasional 

 showers may be responsible for the prevalence of mosquitoes in more 

 ways than one. 



Fifth. That ordinary transient ponds and pools furnish sufficient 

 food for the rapid development of larvae to make the presence of water 

 only necessary for a period of six or eight days to insure the perpet- 

 uation of many species of mosquitoes. On the other hand, water con- 

 taining but little food that is not subject to complete evaporation may 

 prolong the larval life for months. We have observed the life of 

 Stegomyia larvae prolonged under such conditions two months and 

 eleven days. 



Sixth. That the larva? of mosquitoes are not so fastidious in their 

 food habits as they are reputed to be. but that water saturated with 

 foecal matter will shorten the larval period of many species. Steg- 

 omyia under such conditions completed the life cycle in from six to 

 eight days. 



Seventh. That water is not essential to the life of pupa? of many 

 species, so long as the ground upon which they rest is moist. Under 

 the latter condition the pupal period is frequently shortened. This is 

 of importance in connection with the proposed remedy of sweeping 

 gutters in which mosquitoes breed. It also has a bearing upon the 

 transient pools as breeding places for most species. In our experi- 

 ments pupae were kept as long as three days upon moist cotton before 

 emerging. 



Eighth. That most larvae and pupae can remain under water a suffi- 

 cient length of time to be able to survive in cisterns full of water, and 

 that the habit of larvae, some at least, of bringing to the surface more 

 food than can be devoured at once assists a colony of specimens to 

 procure food without having to go to the bottom for individual feed- 

 ings. The data associated with the cisterns as chief factors in 

 mosquito production is not sufficient to draw permanent conclusions. 

 One thing is certain, that water blocked in gutters of buildings by 



