318 



THE AMEBIC AN NATURALIST 



[Vol. LII 



to breed for definite degrees of production, for it can be 

 shown that egg production depends on several more or 

 less independent internal factors and that the same num- 

 ber of eggs may result from the action of different sets 

 of factors. It follows, therefore, that each factor must 

 be studied separately, both from the physiological and 

 genetic standpoints. 



4. The factors reviewed are: date of first egg, age at 

 first egg, growth, rhythm and rate of production, includ- 

 ing here Pearl's genetic factors L 1 and L 2 , broodiness, 

 moult, cycles, persistence of production in the autumn, 

 and stamina. 



5. Date of first egg is shown to depend on the time of 

 hatching, the rate of growth of the young birds and some 

 elements, at present unknown, that determine the attain- 

 ment of sexual maturitj*. On the average it has been 

 found that those individuals that lay early in the fall 

 (October) lay more winter eggs than those that begin to 

 lay later. 



6. On the average, pullets that lay relatively early (6 

 to 7 months) in life lay more eggs than those that lay at 

 a later period (8, 9, or more months) in life, other things 

 being equal. The variability in age at first egg appears 

 to be much greater for our Rhode Island Eeds than for 

 Pearl's Barred Plymouth Rocks. 



7. Birds that lay rapidly, other things being equal, lay 

 more eggs than those that lay more slowly. 



8. Some birds (true mediocre producers) lay very 

 slowly and irregularly, producing only a few eggs (1-10 

 or thereabouts) per month. Others (true high producers) 

 lay much better (15-28 eggs per month). 



9. The effect of the age at which the first egg is pro- 

 duced on winter egg production is such that numerical 

 results, similar to those given by true mediocre pro- 

 ducers, may result. 



10. Some pullets lay continuously or nearly so, for 

 long periods of time. Others lay relatively rapidly, but 

 lay in cycles with a period of rest in between. These rest 



