224 THE AMERICAN NATURALIST [Vol. LII 



ever, have an irregular rhythm. While the observed 

 rhythm is rarely entirely regular, yet each hen tends to 

 produce eggs according to a rhythm that is character- 

 istic to a certain limited degree for that individual. 

 Superimposed on the daily rhythm are evidences of other 

 rhythms having a beat measured by months or years. 

 Although from another standpoint egg production is a 

 more or less continuous process, at least in so far as the 

 growth of the yolk is concerned, even though the fluc- 

 tuations in the activity of the albumen and shell glands 

 may be more pronounced, the rhythm may be considered 

 as it appears on the record sheets, i. e., the rhythm 

 shown in the deposition of the eggs. Various types of 

 rhythm have been observed. If, as a working basis, it 

 be assumed that an egg a day represents a standard 

 rhythm, although this high rhythm is rarely reached for 

 extended periods, it will be found that some hens lay 

 every other da}', or we may say a one half rhythm, others 

 two thirds, i. e., two days out of three, others three 

 fourths and so on. The three fourths or four fifths 

 rhythm is common among most good layers. Occasion- 

 ally the series may be repeated without the intervention 

 of a zero day as is shown by the time of day the eggs are 

 laid, for if the time of day at which the eggs are collected 

 from the trapnests is recorded, the rhythm is shown even 

 better than by the daily records. It has been our prac- 

 tise to visit the nests about every hour and a half and to 

 record the time the eggs were gathered in units of a half 

 hour. Thus the approximate time that each hen drops 

 her egg is known. Rhythm, as shown by the time of day 

 a hen lays her eggs, is an index of the essential con- 

 tinuity of the activities of the ovary in the growth of the 

 ova, rather than of any rhythm in its activity, since the 

 interval between eggs is more uniform than when the 

 daily record only is used. One may perhaps infer that 

 there is some rhythm in the activities of the oviduct since 

 it is known that the stimuli for its activity comes from 

 the presence of the yolk in its lumen. However this may 



