500 
Bulletin No. 162.—1915. 
those more nearly of a size and thus having more nearly equal 
opportunities. In this way we undoubtedly save many birds which 
would otherwise die of starvation or be crowded from the nest by their 
more fortunate nestmates. 
From the foregoing we may conclude then that in all probability 
the time required for incubation by the two eggs is the same, but 
although A is laid nearly two full days before B, it receives on the 
average the equivalent of only about a half-dav of incubation before 
B is laid, so that its mean time of hatching is only a half-day before 
that of B. From the standpoint of the welfare of the second squab 
it would probably be better if this interval were still shorter, so that 
the eggs should hatch essentially at the same time. To this extent 
the instinct which allows A to be incubated at all in advance of B is 
imperfect. On the other hand, domesticated birds at any rate often 
breed during such cold weather that the first egg would freeze if it 
were not protected at all. 
“Control of Sex” in Pigeons* 
Practically all of the various factors which have been held by the 
poultryman to determine sex in poultry, have been put forward for 
pigeons as well. These include such things as size and shape of egg, 
position and size of the air space, and the like. Such theories in the 
past have admittedly had no adequate experimental basis, nor have 
facts in their support been adduced which could stand the test of 
scientific proof. More recentlv, however, certain assertions have 
been made by Biddle as to the control of sex in pigeons, but the 
data on which these statements rest have not as yet been published 
so far as we are aware. Riddle (1914) states definitely and cate¬ 
gorically, however, that “By his method of controlling sex in pigeons 
Whitman showed (1) that the first young of the season (spring and 
early summer) were nearly all males, and young hatched from the 
later eggs of the season were nearly all females; (2) that if the two 
sexes arise from the two eggs of any one clutch, that it is in nearly all 
cases the first egg which produces the male, and the second egg of the 
