232 
The fact that a certain degree of warmth is necessary for develop- 
ment of animal and vegetable life and that the rate of development is 
hastened by warm weather and retarded by cool weather has apparently 
always been known, but it is only within recent years that efforts have 
been made to ascertain the relative effects of different degrees of 
temperature. 
ee 
ZONES OF TEMPERATURE 
The entire range of temperature may be divided into six zones with 
respect to life and development, as shown below: 
eT a ni, 
Zone 64 Fatal temperatures; fatality due to heat. 
L 
Minimum high fatal degree |— 
Tone 5 J Estivation temperatures; not fatal, but 
unfavorable for development. 
Zero of estivation = 
Temperatures stimulating development, 
Zone 4+ the rate of development decreasing as 
the temperature rises. 
Degree of maximum rate | 
development r 5 ‘ 
me P Temperatures stimulating development, 
Zone 34 the rate of development increasing as 
the temperature rises. : 3 
L 
Zero of development bere bo 5 
P E Hibernating temperatures; not fatal, but 
Zone 24 unfavorable for development. . 
Maximum low fatal degree ~|—_ ip 
Fatal temperatures; fatality due to lack 5 
Zone 1 : 
of heat. 
The limits of these zones differ for different species, for different 
stages of the same species, and for different phases of the same stage of 
the same species. 4 
The limits of the zones of temperature of a species will be affected 
by the latitude to which it is acclimated, and it is possible that they will — 
vary for individuals of the same species which are acclimated to different — 
latitudes. Generally speaking, the limiting temperatures of the zones of — 
species in low latitudes may be expected to be higher than of species in 
higher latitudes. The temperature at which an insect comes out of hiber- 
nation is in many cases quite different from that at which it becomes 
dormant in the latter part of the season, because heredity has an impor- 
tant influence in. determining the time when insects begin the dormant 
period which lasts through the winter. 
The temperatures on which these studies are based fall within zones — 
2, 3, and 4, the purpose being to determine for the codling-moth the zero 
of development, or the point at which development begins in spring as __ 
