492 
Bulletin Xo. 162. — 1915. 
Feb. Mar. Apr. May June July 
Fig. 4. Decrease in monthly mean interval between laying of the two eggs of a set, from 
February to July, 19US, inclusive. 
It is unfortunate that records were not obtained for the remaining 
months of the year so that we might know whether the interval 
would continue to decrease or whether it would shorten again as the 
season progressed. The latter seems the more probable assumption, 
but in the absence of further records there is nothing to test it. Two 
possible explanations suggest themselves to account for the pro¬ 
gressive shortening of the mean interval between laying of A and 
B from February to July. In the first place it is possible that this 
change is simply a reaction to temperature conditions, the physio¬ 
logical processes of the bird being accelerated and the interval 
correspondingly shortened in response to the warmer weather as 
the season advances. It seems rather more probable, however, that 
1 lie physiological change in ovulating activity is directly related to 
the normal cycle cf egg production in the pigeon. In domesticated 
pigeons the cycle of egg production undoubtedly extends over a 
longer period than it does in the wild state, as is the case also in the 
domestic fowl. Whether, in pigeons, this is a result of selection, 
direct or indirect, we do not know. At any rate the normal season 
of egg production may be assumed as in the spring or early summer. 
With the extension of the season we might expect the highest activity 
of the physiological processes of egg production to occur at the normal 
