300 WALLACE CRAIG 
The utility of this time adjustment in pigeons seems obvious. 
The male pigeon takes his turn daily in the duty of incubation: 
hence the female must not lay the eggs before he is ready to sit. 
This aspect of the matter, which has to do with pigeon sociology, 
has already been treated elsewhere (Craig ’08) and will be dis- 
cussed more fully in a book dealing with pigeon behavior. The 
present paper is to show, not why the male should determine the 
time of oviposition, but how he does determine it. 
The thesis of the present paper is, that the influence of the male 
in inducing oviposition is a psychological influence; that the stim- 
ulus to oviposition is not the introduction of sperm, for the male 
ean cause the female to lay even though he does not copulate with 
her. This is easily proven by an experiment, which requires only 
pigeons, patience, and time, and I shall now recount seven repe- 
titions of such experiment, the first two being accidental cases, 
the other five being trials designed and carried out on purpose to 
test the thesis. 
Case 1 (1903). In the spring of 1903 I brought together a vir- 
gin female dove (individual female no. 7, the species in all these 
trials being the blonde ring-dove, Turtur risorius) and a young 
inexperienced male, intending simply that they should mate in 
the normal manner. The young male played up to the female, but 
due to his inexperience and to other causes which need not be dis- 
cussed here, his mating behavior was imperfect and he did not 
copulate with her. Nevertheless, in due time (six days) she laid 
an egg, and a second egg, as usual, forty hourslater. This was the 
first intimation to me that a male bird can stimulate the female to 
lay, without copulating with her. Such an explanationseemed 
so absurd at that time that I dismissed it with the assumption that 
the birds must have copulated unobserved, and I did not even 
test the eggs to see if they were fertile. Looking back on that 
case now, however, and considering the observed behavior of that 
male, I feel reasonably certain that he did not fertilize the eggs 
but simply stimulated oviposition through the psychic (neural) 
channels. 
Case 2 (1904). A female dove (no. 5) had been kept alone ever 
since her mate had died in November, 1903, and as time wore on 
