302 WALLACE CRAIG 
mostly in the afternoon, and are continued for several days in 
succession; hence it is best that the experimenter should be able 
to devote some hours a day for several days in succession to a 
single pair or at most two pairs of birds. Whenever the birds are 
not under surveillance they are shut apart, each in his or her own 
cage. But they should be allowed to come together daily until 
the egg is laid. 
A factor which caused difficulty in one of my trials was the nest. 
In cases 1, 2, 3 and 6, the bird laid without any nest at all (except 
that in case 6 a nest was given just a few hours before the egg was 
deposited). But in case 4 (q.v.) the female refused to lay without 
a nest: it was then necessary to remove the male and make the trial 
again, first giving the female a nest, and waiting long enough to 
prove that the nest alone would not cause her to lay. 
Results of the regular trials 
Case 3 (1907). Female dove, no. 20. This bird had been 
bought recently from a dealer, and it was not known whether she 
had laid earlier in the season. But she was kept isolated for 
some time, during which she showed no inclination to lay. She 
was then given a male in the manner indicated. No nest given. 
June 9. Male allowed in cage of female, and plays up to her. 
June 15. First egg. 
June 17. Second egg. (The second egg was of no special in- 
terest. After the first egg was laid, I generally left the doors 
open, allowing the pair to come together without surveillance.) 
Case 4 (1908). Female, the same. She had not laid since the 
close of last season. No nest given. 
February 4. Male allowed to enter. 
The female was unresponsive and showed by her behavior that 
this time she was holding back for want of anest. This deficiency 
was supplied in the following manner (vide ut supra.) 
February 8. Male taken away to another building. 
March 10. Nest put in cage. Female paid practically no at- 
tention to it. Many days were allowed to pass, in order to make 
sure that the nest alone would not stimulate the female to lay. 
