lines has been accumulated, one must suspend fnal judgment 

 on the question of how much does a bird's weight or size 

 influence its incubation length. 



Age of Female 

 It is well known that pullets of our barnyard fowl lay 

 eggs averaging smaller in size than does the mature hen, 

 and this condition also holds good with pheasant pullets: 

 poultry men know that eggs of mean size and weight from 

 each race of our domestic hen hatch more successfully than 

 do too large or too small eggs, whence it might be held that 

 the age of the female may affect the length of incubation, 

 since it has been shown that the mature hen is apt to lay 

 eggs near the normal for her race, which are more uniformly 

 successful in hatching. Whether or not the larger or the 

 smaller than normal eggs really hatch later or earlier than 

 the average I do not know ; in the absence of definite data 

 in answer to this, the question must be left open and un- 

 decided. Possibly the age of the female really affects the 

 fertility or viability of the egg, and not the incubation 

 length. It is also possible that very old females may exhibit 

 a tendency to a slowing of metabolic intensity, which would 

 unfavorably affect the incubating temperature. 



Condition of Parents 



It is not possible to say, owing to the lack of exact in- 

 formation, if the physical condition of the male has any 

 influence on the length of incubation with the species with 

 which the female does all of the incubating; nevertheless, 

 it is conceivable that old, or immature, or weak males may 

 give the new individual in the Qgg a poor start, entailing 

 perhaps la slower rate of development, resulting in a longer 

 period of incubation. 



There is no doubt in my mind but that poor health in 

 either parent (when both incubate) would result in what 

 amounts to a cooling of the eggs during incubation, and a 

 resulting apparent lengthening of this period, through slug- 

 gish embryonic development, all because of the setting bird's 

 temperature being lower than normal. While several writers 

 mention the physical condition of the parents as being a 

 factor in affecting the length of incubation, none has given 

 any data, experimental or otherwise, in support of the sug- 

 gestion. It must be left open and undecided. 



Conduct of Parents 

 The assiduity (or neglect) of the incubating parents 

 in covering their eggs unquestionably results in the eggs 

 being hatched "on time," or "late," or "not at all." In other 

 words, the length of incubation is unquestionably affected 

 by the incubating bird being frightened from its nest too 



26 



