REPRODUCTION IN DOMESTIC FOWL 111 



known to do with advancing age, and since, as table 1 shows, the 

 small oocytes under 1 mm. in diameter make up the vast majority 

 of all those visible, it follows that we should expect to find more 

 and more visible oocytes as age advances up to an asymptote 

 which represents the complete cessation of all ovarian activity. 

 Presumably, the oldest of the birds here counted was not old 

 enough to have reached this condition of complete ovarian rest. 

 Our general knowledge of ovarian functioning in fowls, from 

 personal observation, would lead to this last conclusion as well 

 as the form of the curve in figure 2. 



Probably the complete curve for visible oocytes on an age base, 

 if we had data to plot it, would be of the shape of a flattened S, 

 with an upper asymptote, representing complete ovarian rest, 

 and a lower zero asymptote representing no visible oocytes at an 

 early age. This is a form of curve which has been found to 

 represent growth phenomena of various sorts. ^ 



EXPERIMENTS ON OVARIAN REGENERATION 



It is well known that the ovary in birds is an organ that re- 

 generates readily and freely after injury. Indeed, this fact con- 

 stitutes one of the chief technical difficulties in making a complete 

 and permanent castration of female birds. At the same time it 

 has been held as a basic biological doctrine that during the life 

 of the individual there neither is nor can be any increase in the 

 number of primary oocytes beyond those originally laid down 

 when the ovary is formed. It occurred to us to make a quantita- 

 tive study of visible oocytes in regenerated fowls ' ovaries to deter- 

 mine to what extent an increase could be brought about in the 

 number of primary oocytes which develop to visible size at the 



^Robertson, T. Brailsford. On the normal rate of growth of an individual 

 and its biochemical significance. Arch, flir Entwickelungsmechanik der Organ- 

 ismen, Bd. 25, S. 581-514. 



Robertson, T. Brailsford. Further remarks on the normal rate of growth 

 of an individual, and its biochemical significance. Arch, fi'ir Entwickelungs- 

 mechanik der Organismen, Bd. 26, S. 108-118. 



Pearl, R., and Reed, Lowell J. On the rate of growth of the population of the 

 United States since 1790 and its mathematical representation. Proc. Nat. Acad. 

 Sci., vol. 6, no. 6, 1920. 



