24 DR. C. G. SELIGMANN AND MR. S. G. SHATTOCK ON THE 
it 
Observations on the plumage and the condition of the Testes. 
These were made on domesticated wild ducks such as are found 
in the London parks and supplied from game-farms. These 
birds are commonly slightly larger than those really wild, but 
they pass through the seasonal changes of plumage in approxi- 
mately the same period, and appear to vary in the time (season) 
of their change no more than do wild birds from England and 
Scotland respectively. We were able to examine a few really 
wild birds caught in decoys in January and February, and found 
no substantial difference in the condition of their testes and that 
of those domesticated, but we did not extend these observations, 
since it appeared probable that the confinement of such birds 
might lead to abnormalities in the onset of their plumage 
changes, and even affect the condition of their reproductive 
glands. 
Before dealing with the changes in the plumage and in the 
sexual glands of adult birds, it will be well briefly to summarize 
the conditions found in young or immature birds, by which we 
mean birds of the year, that have not yet assumed full plumage. 
So defined, the period covers the first five to six months of the 
bird’s life and ends in November or December, In the young 
birds the nestling plumage persists until at least the middle of 
September, about which time a few speckled feathers appear on 
the legs and shoulders, the breast and belly being still unchanged. 
By this time the full complement of flight-feathers has appeared, 
but the feathers themselves are usually not more than half grown. 
The testes of such birds are usually quite small, measuring on an 
average about 10 mm. in length and about 2 mm. in breadth; 
they are firm on section, and yellowish brown in colour. Under 
the microscope the tubuli are found to be small, and with a 
relatively narrow lumen lined with a single layer of cells, between 
which certain larger spheroidal spermatogonia are intercalated. 
In some the cells are two deep. The interstitial stroma is 
very cellular, and, contrasted with the condition found.in the 
fully functional gland, it appears relatively abundant *. There 
is a good deal of individual variation in the external appearance 
of the birds at this time, even a few days making a considerable 
difference. The growth of the birds and the development of the 
plumage proceed rapidly during October, so that by November 
the drakes have attained then full size, and have assumed their 
perfect plumage. The testes become larger and yellowish white 
* We may refer here to the appearance presented by the testes of a freshly- 
caught wild Mallard killed during the last quarter of December. This bird weighed 
1 Ib. 142 ozs.; its testes, which were firm, yellowish in colour, and dry on section, 
together weighed 88 mg: Microscopic sections showed the tubuli to be of small 
size, with narrow lumen, lined with a single or double row of cells, and with larger 
spermatogonia occasionally occurring between the basal cells. There was no sign of 
spermatogenesis. 
