REPRODUCTION IN DOMESTIC FOWL 117 



operated ovaries of the same bird. This excess amounts in the 

 case of the Barred Rocks to 2150 — 1615 = 535, an increase of 

 33 per cent in operated over normal, and in the case of the Cor- 

 nish Indian Games to 2611 —1550 = 1061, an increase of 68 per 

 cent in operated over normal. The excess shown by the Barred 

 Rocks can hardly be regarded as statistically significant, on the 

 basis of the present short series. The fact, however, that both 

 breeds show such a consistent set of results throughout is evi- 

 dence that with a longer Barred Rock series we should get essen- 

 tially the same result as with the present one and with suffi- 

 ciently reduced probable errors to make the difference statis- 

 tically significant. A fair and instructive comparison can be 

 made by lumping together the Barred Rock and Game operated 

 series, and putting the mean total number of visible oocytes 

 produced during life against the mean total number produced by 

 all normal unoperated fowl, excluding the White Leghorns, 

 since our previous results show that this breed has evidently 

 as a breed character a distinctly larger number of visible oocytes 

 than any of the other breeds dealt with. On this basis we have: 



Mean total visible oocytes produced during life by eight 



operated birds 2381±143 



Mean total visible oocytes produced during life by twenty 



normal birds 1793± 79 



Difference 588±163 



Here we see that the difference is 3.6 times its probable error, 

 and hence to be regarded as almost certainly statistically 

 significant. 



Altogether it is believed that we may safely conclude that by 

 inducing by operative means ovarian regeneration in the domestic 

 fowl the total number of primary oocytes which develop to visible 

 size is significantly increased. 



Following these experiments the senior author undertook much 

 more extensive work on repeated ovarian regeneration. In a 

 series of birds of known and highly interesting genetic constitu- 

 tion (F2 birds of a carefully studied cross) a considerable portion 

 of the ovary was removed each autumn for four years. The 

 laying record was kept over this long period, and also careful 



