42 DR. C. G. SELIGMANN AND MR. 8S. G. SHATTOCK ON THE 
on September 12th, 1907, spermatogenesis was in full progress 
in the graft, a condition of activity which does not occur under 
normal conditions at this period of the year. 
In the case of two additional castrated birds (not further re- 
corded in this paper) which were killed between the end of June 
and September 1907, spermatogenesis was likewise taking place in 
similar grafts : 7. e., at a time when in normal birds the testes are 
functionless, at least as regards their external secretion. The 
histological condition found in the grafts in these different birds 
is shown in the following table :-— 
(No. 8m.) Killed: June 1907 (late). 
Condition of grafts : 
One graft about the size of a small gooseberry ; the tubuli are of large size 
and distended with cells; mitotic figures fairly abundant. In the centre of 
one tubule is a group of deeply-stained filaments with bulbous ends, which 
must be considered spermatozoa. 
(No. 39.) Killed: September 12th, 1907. 
Condition of grafts : 
One graft about the size of a large pea. This consists of the epididymis 
and testicular tissue, the tubuli of which are of full size; spermatogenesis is 
in active progress. 
(No. 48.) Killed: September 12th, 1907. 
Condition of grafts : 
One graft the size of a small haricot. The tubuli are large and distended 
with cells; in every tubule spermatogenesis is in full progress. 
(No. 22 bis.) Killed: Mid-September 1907. 
Condition of grafts : 
Graft consists of closely-set tubuli of large size and fullof cells. Spermato- 
genesis with well-developed spermatozoa present in some of the tubes: in 
other tubuli the centre is filled with a vacuolated mass of cell-débris 
without spermatozoa. 
Conclusions. 
I. In the male of the Wild Duck the testes undergo annually 
a series of seasonal changes (as in many other birds), and are 
spermatogenic only during the winter months and early spring. 
Il. The periods of activity and non-activity do not coincide 
with the two seasonal changes in the plumage. 
ITI. The normal passage of the bird from full winter (breeding) 
plumage to its dusky summer (eclipse) plumage is, however, 
delayed if castration is carried out during the months whilst the 
gland is assuming, or has attained, its activity. 
One bird (No. 18) which was castrated in the winter, and in 
which the advent of the succeeding eclipse was delayed the 
following summer, was kept until the summer of the next year. 
