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THE AMEBIC AN NATURALIST [Vol. XLIX 



year ' ' made under the mass-selection system. In the first 

 place in order to make the comparison at all fair the 

 flocks in which the birds were kept when the records were 

 made must be of approximately the same size. It has 

 been conclusively demonstrated by earlier work in the 

 laboratory that egg production becomes reduced as flock 

 size increases. It would be idle to compare the results 

 now where the birds run in flocks of 125 to 150 birds per 

 pen with the "best" of those prior to 1904, when the 

 flocks were never larger than 50 birds each and were some- 

 times smaller. This restricts single year comparisons 

 then to the period after 1904. 



In the second place, if we take the year when the total 

 production was highest, as the "best" year, we shall find, 

 in practically every case, that some particular month or 

 months of this year will fall below the average for that 

 month or months. There are then two alternatives, 

 either, on the one hand, to take for comparison with a 

 single year now that year under the old system of breed- 

 ing which, on the whole, is the best and then make allow- 

 ances for disturbing factors in particular months, or, on 

 the other hand, to compare a single year now, month by 

 month, with an artificial year's record made up by pick 

 ing out the best record of each individual month regard- 

 less of the year in which it occurred or of the size of 

 flock. The second of these comparisons is obviously 

 artificial, since it is continued high production month 

 after month in the same laying year which is important. 

 It is of interest, however, to see the results of the com- 

 parison on both bases. These comparisons are made in 

 Table I. 



The best single year 100-bird pen record in the earlier 

 period is, as already pointed out, that for 1905 -06, having 

 regard to the months here compared (November to July, 

 inclusive). The 100-bird pen of 1904-05 made a better 

 record during the summer than the corresponding pens 

 of 1905-06, but fall considerably below in winter pro- 

 duction. In 1905-06 there was an environmental accident 



