ABSTRACTS. 283 



dary sexual feathers is 'not necessarily dependent upon any 

 normal moult. If "the juvenile feather is removed from the 

 follicle the next feather produced by that follicle will be the 

 secondary sexual feather, and not a feather of the juvenile 

 type. After that all further regenerations are of the sexually 

 differentiated feather. 



The. Measurement oe Changes in the Rate oe Fecundity 

 oE the Individuae Fowl.* 



The purpose of this note is to call attention to a method of 

 measuring and representing graphically changes in the intensity 

 of ovarian activity, as indicated by rate of ovulation, in the 

 domestic fowl. It has been fully established that if one con- 

 siders the egg production records from a group or flock of 

 hens as a whole there are observable regular and distinct 

 cycles in the production. Thus, we have distinguished in 

 former publications between winter, spring and summer cycles 

 of flock production. It has not hitherto been possible to 

 observe precisely or to measure any such cyclical changes 

 (either of long or short period) in the egg production of a sin- 

 gle individual bird, owing to the fact that the production is 

 in discrete units. Yet while the end products of ovarian activ- 

 ity are discrete units there are very strong reasons for suppos- 

 ing that physiologically the elaboration — or production in the 

 broad sense — of eggs by the ovary is a continuous process of 

 secularly changing rate, irather than a ^truly discontinuous 

 process. 



By a simple statistical expedient it is possible to represent 

 the changes in rate of fecundity in an individual bird as a con- 

 tinuous curve, of which the ordinates represent the rates of egg 

 production on a percentage scale (o to 100) at the time inter- 

 val plotted as abscissae. This is done by taking, as the rate 

 of fecundity for any given day Pn, the percentage which the 

 actual number of eggs laid by the bird during the 21 days of 

 which Pn is the central day, is of 21. Put as a formula, if 

 Rp\^ = rate of fecundity (or ovarian activity as indi- 

 cated by ovulation) on the day P^ 



*This is an abstract of a paper by Raymon'd Pearl having the same title 

 published in Science, N. S., Vol. XL, pp. 383-384. 



