202 NATURAL HISTORY SOCIETY OF DUBLIN. 
testicle will be very striking. This circumstance,” he continues, ‘is 
not peculiar to birds, but is common, as far as I yet know, to all ani- 
mals which have their seasons of copulation. In the buck we find the 
testicles are reduced to a very small size in the winter ; and in the Jand 
mouse, mole, &c., this diminution is still more remarkable.’ A Plate 
in Hunter’s ‘‘ Observations on certain parts of the Animal Economy”’ 
shows the gradual increase in size of the testes of the sparrow from 
the middle of winter to the beginning of the breeding season, repre- 
senting the appearance of these glands in the months of January, Fe- 
bruary, March, and April. 
I have not information as to the time of year when the testicles of 
the domestic drake attain the maximum degree of their periodic en- 
largement, nor can I find many observations on the subject; but I am 
inclined to think that it is about midsummer, the time when I dis- 
sected the specimen alluded to this evening, and for the reason that at 
the opposite period of the year, mid-winter, I find the testicles of the 
wild drake very small. To-day (December 3rd, 1868,) I examined 
the bodies of three mallards to ascertain the size of these glands in 
them, and found them extremely small; in one bird, weighing 2 lbs. 
9 oz., the testicles together weighed less than 4$ grains, in another 
weighing 2 lbs. 24 0z., they weighed less than 34 grains. Although 
domestication, and the change of habits it entails, may influence the 
degree of periodical increase, I do not think that it will alter much the 
time of it as long as the wild and domestic drake are living in the same 
climate; therefore I think midwinter to be the time the domestic 
drake’s testicles are smallest, and midsummer when they are largest. It 
is not likely that the testicles of the mallard will ever equal in size those 
of the domestic drake when at their full size; because it has been ob- 
served that the testicles are at all times larger in birds living in 
polygamy than in others ; the domestic drake is practically a polyga- 
mist, although the wild duck is monogamous. It is known that the 
fertility of the duck is increased by domestication, the wild duck laying 
from five to ten eggs,* the tame one in the course of one year from 80 
to 100; and if it may be assumed that the reproductive powers of the 
drake also undergo a similar development from domestication (which is 
a reasonable hypothesis), there is an explanation of the change in his 
nature from monogamy to polygamy and we would expect to find a con- 
comitant development of his sexual organs. Summing up then the 
case of these testes, they may, I think, on the one hand, be at once said 
to be diseased, abnormal in size, and hypertrophied; or, on the other 
hand, the enlargement may be attributed to an unusual degree of their 
natural periodical development. 
Professor E. Prrcevat Wricut, M.D., read ‘‘ Notes or a Tour 
DURING THE SPRING AND SUMMER oF 1868, IN Sicrny anD PoRTUGAL 
Vide end of June Meeting. 
* Darwin, ‘‘ Animals and Plants in Domestication,” vol. ii., p. 112. 
