‘ROLIPSE” PLUMAGE IN THE MALLARD. 25 
in colour, as well as softer, but no juice exudes on section, and 
spermatozoa are absent. At this time of the year, 7.e.at the end 
of November and December, there is no marked and constant 
difference between the testes of the young birds of the year that 
have but just assumed their winter plumage for the first time, 
and the testes of older birds that are passing into their full 
plumage for the second or third time. But since our observations 
lead us to think that the changes in the testes may take place 
rather more rapidly and regularly, and perhaps a little earlier, in 
the older birds, we confined our observations to birds which had 
passed through at least one full change of plumage. 
In order to make clear the significance of the plumage-changes 
in normal and in partially castrated adult. birds, recorded 
below, we may give asummary of those which naturally occur in 
the male wild duck. 
Normally in the adult Mallard (Anas boscas), which, it is 
assumed, has bred early in the spring, the curly tail-feathers are 
lost, and the moult of the body-feathers begins late in May or 
early in June. By the beginning of July the assumption of the 
dusky, summer, or “eclipse” plumage should be tolerably com- 
plete, though the moult of the flight-feathers has not, as a rule, 
begun, these being lost usually by the middle of the month. The 
eclipse plumage persists throughout August, during which month 
the Mallard, the Duck, and the young are externally very much 
alike. By the middle of September the curly feathers have 
usually appeared in the tail of the Mallard, and the bird passes 
from its summer to its winter plumage, which does not, however, 
reach its full beauty until about midwinter. 
The period of the year at which the plumage changes take 
place varies with the latitude. In the British Museum (Natural 
History) there is the skin of a bird in full male plumage with 
curl feathers in the tail, which was killed at Shanghai (lat. 31° N.) 
on August 28th, 1884. The skin of another bird, killed on 
December 11th, 1879, at Nagasaki (lat. 33° N.), is in partial 
eclipse, with many brown feathers on the vertex, and eclipse 
feathers in the breast; while the skin of a third bird, from 
Wuhu, on the Yangtsze, killed.in January 1885, has similar, but 
less well marked, remains of the eclipse plumage on the breast 
and head. 
A Table showing the condition of Plumage and that of the 
Testicles at each month of the year. 
January 30th. Full winter plumage. 
Weight of both testes, 3850 mg.:; each gland is about 23 mm. in greatest 
length, of a yellowish-white colour and soft; fluid can be scraped from the 
cut surface, but it does not ooze naturally. 
(In a bird killed January 23rd, the testicular tubuli were small; with well- 
defined lumen; cells about two deep; no spermatogenesis.) 
