Mr Heape, Note on the influence of extraneous forces, etc. 201 
Note on the influence of extraneous forces upon the proportion of 
the sexes produced by Canaries. By Walter Heape, M.A., F.R.S., 
Trinity College, Cambridge. 
[ Received 1 May 1907.] 
The careful records on which the following note is based 
were very kindly supplied to me by two breeders of canaries, 
Mr Needham and Mr Gentry. 
Their results show a remarkable difference in the proportion of 
the sexes of the young birds produced in these two aviaries, which 
is consistent both in detail and in the totals. 
Such consistent variation, when considered in relation to the 
food supplied and to the temperature and surroundings to which 
the birds were subjected, may be interpreted as evidence of the 
exercise of extraneous forces on the proportion of the sexes pro- 
duced and of selective action on the generative elements dehisced 
by the parent birds. 
In a former paper (“ Note on the proportion of the sexes in 
Dogs,” Proc. Camb. Philosoph. Soc., 1907) I have indicated my 
reasons for believing that extraneous forces do influence the 
proportion of the sexes produced by certain animals, and the 
evidence now presented is, I judge, confirmatory of that view. 
In the following account Mr Needham’s records will be referred 
to as N, Mr Gentry’s as G. 
Results as sh own in Table I. 
N. During the years 1888 — 1893, 11 cocks and 22 hens were 
bred from. One cock and one hen were “London Fancy” breed, 
a second hen was cross bred, all the rest were “Lizard” canaries. 
These birds formed 71 nests and laid 313 eggs, from which 87 
cocks and 113 hens were hatched — a total of 200 chicks. That is, 
with a loss of 36'l°/ 0 of eggs the proportion of the sexes produced 
was at the rate of 76’99 cocks per 100 hens. 
G. During the year 1892 bred from 4 cocks and 8 hens, all of 
which were “ Lizards ” with the exception of one cross bred hen. 
These birds made 20 nests, laid 84 eggs from which 53 cocks 
and 15 hens, a total of 68 chicks, were hatched. That is, with a 
loss of 19'05°/ o of eggs the proportion of the sexes produced was at 
the rate of 353’3 cocks per 100 hens. 
But certain data are available where no loss of eggs occurred. 
N had 4 cocks and 9 hens making 11 nests and laying 48 eggs, 
all of which were hatched. These produced 22 cocks and 26 hens, 
that is at the rate of 8461 cocks per 100 hens. 
G had 4 cocks and 6 hens making 11 nests and laying 48 eggs, 
all of which were hatched. These produced 35 cocks and 13 hens, 
that is at the rate of 269‘23 cocks per 100 hens. 
Thus G’s birds hatched, and must have produced, a very large 
excess of cocks, while iV’s birds are responsible for a marked 
excess of hens. 
VOL. XIV. PT. II. 
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