272 EXPERIMENT STATION EECOED. 



distributions are usually uniniodal and unsyimnetrical. The asymmetry or 

 skewness. when it exists, is always in the negative direction; that is, the modal 

 egg production is always larger than the mean egg production, (c) The amount 

 of variation in egg pi'oduction is both absolutely and relatively large. The 

 mean value of the coefficient of variation from all our data is about 34 per cent. 

 (d) Variation in egg production, so far as our statistics show, belongs to the 

 type of continuous, so-called ' fluctuating ' variation. 



"Analytically considered, such of the variation polygons as are skew are 

 found to conform to Pearson's Type I curve. The symmetrical distributions 

 belong either to his Type II or the normal curve of errors. The range of varia- 

 tion is in nearly all cases greatly overestimated by the theoretical curves. It 

 is pointed out that this appears to be a characteristic of fecundity curves 

 frequently. 



"It is shown that during the period covered by the statistics (1899-1907), 

 which covers practically the whole period of the breeding experiment, there has 

 been, apart from fluctuations up and down in individual years, a small but 

 steady decrease in the mean or average annual egg production. 



"During the same period (1S99-1907) the variability in annual egg produc- 

 tion has not sensibly changed. There have been chance fluctuations up and 

 down in indi\idual years, but there has been no steady trend toward lower or 

 higher variability. The same statement applies to the skewness of the distribu- 

 tions in the period covered by the investigation. 



"The percentage of extremely high layers (producing more than 195 eggs in 

 the pullet year) in the flock decreased during the period from 1899 to 1907. 

 The percentage of exceptionally poor layers (producing less than 45 eggs in the 

 pullet year) in the flock increased during the same period. 



" The general characteristics of variation in annual egg production in AVhife 

 Wyandottes are essentially similar to those described above for variation m 

 liarred I'lymouth liocks. 



"Evidence from the lit(>rature is presented tending to show (a) that it is 

 possible to get average annual egg yields higher than any of those which have 

 been observed at the Maine Exi^eriment Station, and {h) that records exist 

 showing that in exceptional cases average annual egg yields were obtained dur- 

 ing the middle and earlier half of last century which were just as high as any 

 we now know. 



" When the laying hens were kept in flocks of 100 birds each the average 

 annual egg production per bird was distinctly and significantly lower than 

 when they were kept in flocks of 50 birds each, though the numljer of square 

 feet of floor space per bird was the same in the two cases and all other environ- 

 mental conditions were made as nearly as possible identical. 



" Laying birds kept in flocks of 150 birds each, and with somewhat less 

 floor space per bird than those kept in flocks of 50 and 100 birds each, have In 

 every case an average annual egg production signiflcantly smaller than that 

 of the birds kept in smaller flocks. It is pointed out that great caution must 

 be shown in drawing practical conclusions from these results relative to hous- 

 ing, because we are here dealing only with annual egg production. 



" Those conditions of housing and flock size which tend to lower the mean 

 annual egg production are found to .tend lo increase the variability of the pro- 

 duction, so that poor producing flocks are at the same time flocks very variable 

 in production, and vice versa. 



" Egg production in the second laying year is found, on the basis of rather 

 meager data, to average about a third lower and to be distinctly more variable 

 than thai in the pullet year. There is no sensible correlation between the pro- 

 duction of the first and second year. 



