No. 581] 



INHERITANCE OF FECUNDITY 



3< 19 



completion. These 192 birds were divided among three 

 flocks of 125 each, the other birds in each flock being cross- 

 breds of various sorts. 



It is possible to compare these 1913-14 flock with the 

 old records during nine months of the year only. The 

 reason for this is found in the fact that the trap-nesting 

 season is, under the present system of management, 

 brought to a close with August. Furthermore a record is 

 now kept of the laying of the pullets in October at the 

 beginning of the year, whereas formerly the season's 

 records did not begin until November 1. This comparison 

 is made in Table I. Also in this table the production for 

 1913-14 is compared with the best single year during the 

 mass selection experiment, when anything approaching a 

 corresponding number of bird- were included, 4 and for 

 which all environmental conditions may be regarded as 

 approximately normal. 5 The single year records which 

 come nearest to fulfilling all the conditions for a fair com- 

 parison with 1913-14 are those for the 100-bird pens in 

 tin- laying year 1905-06. There were two such pens and 

 182 birds survived through the year. There was one 

 small environmental accident in that year which reduced 

 the production in May somewhat. 6 There were adverse 

 environmental influences in 1913 probably quite as effect- 

 ive in reducing production as anything that operated in 

 1905-06. The seasonal conditions, size of flock, etc., were 

 all fairly closely comparable with those obtaining in 1913- 

 14. At that time (1905-06) the flock had been under con- 

 tinuous mass selection for eight years. 



There are a number of difficulties in the way of making 

 a comparison between any single year now, and the "best 



