inheritance; op fecundity in domestic eowIv. 303 



(2) The upper limit of the winter period at March i is arbi- 

 trary, and only approximately coincides with the biological 

 reality. Actually with most birds the spring or reproductive 

 cycle of production (cf. 37) begins in the latter part of Febru- 

 ary. In handling the material it has been found necessary (for 

 reasons which will be obvious upon consideration of the mat- 

 ter) to take a fixed date for the beginning of the spring cycle 

 of laying and the ending of the winter cycle. The records of 

 the Station prior to 1908 are tabulated only for months (the 

 daily records unfortunately having been destroyed before I 

 took charge of the work), and on this account it is necessary to 

 take the working limit of ihe winter cycle at the end of a calen- 

 der month. Since March i comes the nearest to the biological 

 limit of any date which is also the beginning of a calendar 

 month it has been chosen. The error introduced by taking this 

 arbitrary date for a point which really shifts within rather 

 narrow limits is, on the average, small. However, it must be 

 recognized as a disturbing element in the individual case. Thus, 

 some birds which really lack any genetic factor for winter 

 production will begin to lay in the last days of February, and 

 consequently on the arbitrary 'March i' basis will actually be 

 credited with a small winter production. This will tend to make 

 the number of zero birds observed smaller than that expected on 

 theory. 



(3) Owing to the factors of environmental influence and so- 

 matic fluctuations it is difficult to classify birds in respect to 

 fecundity, which have winter records near the boundary point, 

 30 eggs. Some birds bearing genes for a production of under 

 30 eggs will actually lay 31, or 32, or 33, etc. The point con- 

 sidered under (2) again comes into play here. A bird may 

 bear the genes for an 'Under 30' record, and actually make such 

 a record during the true biological winter cycle or period. But 

 if it begins the spring cycle early (i. e., before March i) it gets 

 credited on its winter: record with the eggs which it lays in the 

 last days of February, but which biologically belong with the 

 spring production, and in this way its apparent winter record 

 becomes something over 30. while its real winter production 

 was under 30. 



All these factors obscure and render difficult the critical clas- 

 sific?tion anrl interpretation of the results. Allowance must be 

 made for t^.'eir influence. 



