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The term “generation” is used to designate a group of insects in all 
the four stages from egg to adult, all equally removed by descent from a 
given insect or group of insects, except that the term “hibernating genera- 
tion” is used for all the insects which hibernate, regardless of the 
generations to which they belonged the preceding year. 
The term “brood” is used to designate all the individuals of one of 
the stages of a generation, as, brood of eggs, brood of larve, etc. The 
terms “first brood”, ‘‘second brood”, and “third brood” are used to desig- 
nate the eggs, larve, pupz, or adults of successive generations. 
The “theoretical zero of development” is the temperature at which 
development begins when the temperature is rising and at which it ceases 
when the temperature is falling. 
The “degree of maximum rate of development” is the temperature 
at which development proceeds most rapidly. 
The “day-degree” is the unit used for measuring accumulations of 
temperature, and is equivalent to a temperature of one degree maintained 
for 24 hours. 
“Effective day-degrees” are day-degrees above the zero of develop- 
ment, after necessary corrections have been made for retardation due to 
temperatures above the degree of maximum rate of development. This 
correction is made by subtracting twice the day-degrees above the 
degree of maximum rate from the total day-degrees above the zero of 
development. 
The codling-moth passes the winter in the larval stage. The over- 
wintering larve belong principally to the second and third generations of 
the preceding year, but for convenience in discussing the seasonal history 
we designate them as the hibernating generation. The generations which 
descend from the hibernating generation are designated as the “first 
generation’, the “second generation”, etc. In accordance with the fore- 
going definitions we have the following relations of generations and 
broods: 
The hibernating generation, con- The second generation, consist- 
sisting of ing of 
the hibernating larve, the.second brood of eggs, 
the first brood of pupz, and the second brood of larve, 
the first brood of adults. the third brood of pupe, and 
The first generation, consisting of the third brood of adults. 
the first brood of eggs, The third generation, consisting of 
the first brood of larve, the third brood of eggs, 
the second brood of pupe, and the third brood of larve, etc. 
the second brood of adults. 
In the case of insects which pass the winter as adults, the number 
of the broods will agree with the number of the generations to which they 
belong, but in the case of those that pass the winter in the egg, larval, or 
pupal stage, these numbers will not agree in all the broods. 
