CLIMATE AND DISTRIBUTION 293 
this area, perhaps here and there and not always in the same place every winter. 
From these foci the summer dispersal is no doubt much facilitated. 
The temporary distribution is determined by the means of carriage that hap- 
pen to be available. The insects do not fly far, as we have shown, but are readily 
carried in conveyances. Thus the species may continue to exist for a time 
wherever it may be carried while the temperature remains about 80°. 
These facts have not been generally taken into account in discussing the distri- 
bution of Aédes calopus, and so the temporary and permanent habitats of this 
insect have not been separated. It is impossible to do so from records of cap- 
tured specimens only, consequently these distributions can not be exactly 
mapped. 
When Theobald published the first two volumes of his Monograph of the 
Culicide of the World, in 1901, he stated roughly that this insect, which at that 
time was not known to him as the yellow-fever mosquito, ranged from 38° south 
latitude to 38° north latitude, and his map upon page 292, vol. 1, indicated a 
general distribution throughout eastern Australia, western New Guinea, all of 
Celebes and farther India, southern Japan, eastern Hindostan, the Seychelles, 
southeastern Africa, the African west coast, including Senegambia and Lagos, 
Spain, southern Italy, the east coast of South America from British Guiana to 
the La Plata River, Panama, Belize, all of Cuba, Jamaica, Haiti, Bermuda, 
and all of the southern United States. In vol. iii of his monograph, published 
in 1903, he adds certain other localities. 
In No. 46, vol. xviii, of the public health reports of the Public Health and 
Marine-Hospital Service, published November 13, 1903, and subsequently re- 
vised to September 10, 1905, one of the writers (Howard) published a long list 
of additional localities. All of these are covered by the general statement of the 
distribution given above. All the exact localities observed by us will be found 
under the heading of Aédes calopus in the systematic part of this work. 
The foregoing consideration of the temperature conditions governing the 
breeding of Aédes calopus explain why epidemics of yellow fever have occurred 
on the Atlantic coast of North America even as far north as Montreal, and 
may again occur, whereas no epidemic has occurred on the Pacific coast, nor 
is it possible for one to occur. The summer temperature on the Atlantic coast 
is for long periods at or above 80° both day and night, so that the mosquito, once 
carried by ship or otherwise from regions of its permanent occurrence, may breed 
in large numbers in our cities. It needs then only the introduction of cases of 
yellow fever to start an epidemic. 
On the Pacific coast, on the other hand, the nights are so cold that the mos- 
quito can not survive. It is as regularly imported into Pacific coast ports as into 
Atlantic ones. We have records of specimens taken at San Diego and San Fran- 
cisco. It breeds permanently in all the west coast Mexican seaports and must be 
frequently brought to the Californian coast. Yet it has never been known to 
breed there. This seems at first sight strange, since the mean annual tem- 
perature of southern California is much above that of eastern cities where epi- 
demics have occurred. In San Diego and Los Angeles one sees tropical vege- 
