ON THE “ ECLIPSE” PLUMAGE IN THE MALLARD, 23 
2. Observations made to ascertain whether any Relation 
subsists between the Seasonal Assumption of the 
“ Helipse ” Plumage in the Mallard (Anas boscas) and 
the functions of the Testicle*. By C. G. Srniamany, 
F.Z.S., and 8. G. SHarrocr. 
[Received December 20, 1913 : Read February 17, 1914. | 
(Text-figures 1-6.) 
INDEX. 
Physiology and Variation. 
The observations herein set forth were made with the object of 
ascertaining whether any relation exists between the condition 
of the testicle and the seasonal assumption of the eclipse plumage 
in the male of the Wild Duck or Mallard (Anas boscas). 
Although the seasonal changes are well known and were fully 
described many years ago by Waterton, with whom the term 
‘« eclipse ” originated 7, it does not appear that any observations 
have been made on the condition of the testes accompanying 
the change. 
What we wished to determine was, whether the assumption of 
the male plumage corresponded with the advent of spermato- 
genesis, and whether the occurrence of the “ eclipse” is associated 
with retrogressive changes in the sexual gland. 
We may point out that the interest attaching to this question 
is increased if the pairing habits of the wild duck and some other 
common birds be considered. The cockerel of the common fowl, 
for example, is sexually potent as soon as its external characters 
are declared (so that poultry breeders are careful to separate 
the cockerels from the pullets as soon as the former begin to 
show male plumage), but in the pheasant, although full male 
plumage is assumed in the autumn, no pairing (or any mani- 
festation of the sexual instinct) takes place until the spring. In 
the wild duck the birds pair in the autumn or early winter, after 
the male assumes full plumage, but copulation does not occur 
until the spring is advanced. 
Our observations fall into two series :-— 
1. Simultaneous observations on the plumage and the condition 
of the testes in a series of Wild Ducks throughout the year. 
2. Observations on Wild Ducks from which the testicles have 
been removed. 
* The expenses connected with this work were defrayed by a grant from the 
Royal Society, London. 
+ W. Yarrell, ‘ History of British Birds,’ vol, iii. p. 175, 
