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THE AMERICAN NATURALIST [Vol. LII 



out of the class of mediocre producers, when measured by 

 a specific number of eggs, into that of the high class. If, 

 then, one is dealing with a flock in which these degrees of 

 maturity exist, it is evident that extreme care must be 

 taken to avoid confusion due to differences in maturity 

 or rate of growth. 



Differences in maturity may be observed among the 

 males as well as the females, although there is no precise 

 objective point at which a male may be said to have be- 

 come mature, which is comparable to the first egg of a 

 pullet. On the whole, the larger birds tend to mature 

 later than the smaller, though the rule is by no means 

 rigid, since some small birds grow slowly while some 

 large birds grow quickly. Since age at first egg is so 

 large a factor in determining the kind of record a bird 

 makes, one has a physiological character in the male of 

 considerable value as an index of his capacity for produc- 

 ing females that will mature at a given age. 



The age of a bird when she produces her first egg does 

 not coincide necessarily with bodily maturity, theoreti- 

 cally at least, although it seems that a certain size must 

 be reached before the bird can begin to lay. On the other 

 hand, the relation between body size and age at first egg 

 as frequently encountered is of a sort such that the larger 

 birds tend to lay at a later absolute age than the smaller 

 ones hatched the same day. There are many exceptions, 

 however, to this rule. It would, perhaps, be better ex- 

 pressed to say that more heavy birds lay late in life than 

 early, while more of the lighter birds lay early than late. 

 For one of the flocks, the coefficient of correlation between 

 age at first egg and weight has been calculated and found 

 to have a value of + .5473 + .0216. 



The influence of the date at which the first egg is produced 

 as well as the relation of age at first egg to the number of 

 eggs laid during the winter months is shown in the series 

 of records shown in Figs. 3 and 4 (Page 78). These 

 records have been selected in such a way that the rate of 

 production is nearly constant, although the date of hatch- 



