ADAPTATION IN BREEDING HABITS 283 



However, if the eggs are kept in low temperatures for some months there will be 

 a considerable loss. In one case eggs which had been exposed to night tempera- 

 tures of from 10° to 20° C. (50°-68° F.) for 70 days were placed in a proper 

 temperature for hatching and only one-twentieth of them produced larvas. The 

 French observers concluded from their results that eggs subjected to low tem- 

 peratures for some months will perish. 



The Brazilian investigators made careful experiments with high, as well as 

 low, temperatures. Eggs taken from the water the day after they were laid were 

 placed for five minutes in an oven regulated to temperatures of from 37° to 47° 

 C. (99°-117° F.) ; when afterwards placed in water they hatched after 48 hours. 

 The larvas from these eggs developed in a normal manner and the first imago, a 

 female, issued seven days after the hatching of the eggs. Exposed to a tem- 

 perature above 48° C. (118° F.) for five minutes the eggs failed to hatch for 

 the most part ; the few that hatched only did so after from four to six days. At 

 49° C. (122° F.) and above the eggs would no longer develop. 



Peryassii records the following experiments regarding the effect of cold on 

 the eggs. Eggs frozen in a mixture of salt and ice for 30 minutes failed to 

 develop. In another experiment 150 recently laid eggs were frozen for one hour, 

 and then, after being allowed to thaw out, were placed in an oven at a tempera- 

 ture of 35° C. (95° F.) ; they began to hatch on the sixth day. In still another 

 experiment eggs, also recently laid, were frozen for half an hour on two suc- 

 cessive days; they hatched on the third day. 



Experiments were further conducted on the effects of varvdng degrees of 

 salinity of the water on the hatching of the eggs. Eggs would not hatch in pure 

 sea-water. Female calopiis were induced to lay their eggs in a mixture of fresh 

 water with 30 to 35 per cent sea-water; these eggs hatched and the larvge de- 

 veloped to imagos. With 40 per cent of sea-water the eggs hatched but the 

 larvae did not develop. 



BREEDIXG-PLACES. 



There seems to be a strong probability that Aedes calopus was originally a 

 tree-hole breeding mosquito. There are several arguments in favor of this con- 

 clusion. The mosquitoes which come closest to it in general habits are tree 

 breeders. Calopus itself will breed in tree-holes when such happen to be near 

 human habitations. Tree-hole breeding forms, like Aedes triseriatiLS, will breed 

 also, when there are human habitations near their original home, in rain-water 

 barrels and other domestic accumulations of water such as seem now to be the 

 normal breeding-places of calopus. The tree-hole breeding forms, like tri- 

 seriatus and mediovittata, are continuous breeders just as is calopus, whereas 

 the forms breeding in temporary puddles and swamps are more or less periodical 

 in their occurrence, depending to a great extent upon rainfall. The egg-laying 

 habits, as just described, are in accordance with this view. Originally, then, a 

 tree-hole species, calopus has so perfectly adapted itself to human civilization 

 that it has become a true domestic form and practically dependent for its ex- 

 istence upon the conditions that surround human habitations. This dependency 



