30 DR. C. G. SELIGMANN AND MR. S. G. SHATTOCK ON THE 
whereas castration performed in July, while the testicles are 
retrograding and the bird is in eclipse plumage, produces 
no corresponding delay. Furthermore, the small size of the 
“ ovafts,” or regenerated tissue, in birds killed from nine to ten 
months after operation, would indicate that the amount of 
testicular tissue, regenerated, and exerting its influence on the 
bird during the early months after the operation, must have 
been extremely small. 
Our observations fall into two series according as the testes 
were removed, (A) while the bird was in full winter plumage, or 
(B) during eclipse. 
(A.) The Results of Castration when performed on Birds 
whilst in full Winter Plumage. 
No. 18.) (Text-fig. 1.) Bird in full winter plumage; castrated in 
December 1906. The testes removed showed active mitosis and 
spermatogenesis in many tubuli. 
June 9th, 1907.—Bird in full plumage, with glossy vertex, and 
one very glossy feather in tail*. The only sign of approaching 
eclipse 1s a slight brownish-yellow tinting of some of the speckled 
feathers on the belly. 
July 11th, 1907.—Full plumage unmodified except that there 
is a diffuse light brown coloration of the abdomen: this is not 
due to any growth of new feathers but to a pigmentary modi- 
fication in the old. There are two curl feathers in the tail and a 
third forming. 
July 28th, 1907.—The general appearance of the bird is still 
that of a male in full plumage; and the white ring on the neck 
is as marked as ever it was, but there are a few brown feathers 
on the cheeks (first noticed on July 23rd), and a strong flush of 
eclipse feathers in the maroon area on the breast, which is 
becoming somewhat lighter in colour. A number of eclipse 
feathers are obvious upon the abdomen; these are mostly old 
feathers in which pigment changes have taken place; the great 
majority of feathers on the abdomen are still vermiculated. 
There are a few new eclipse feathers in the scapular region. The 
tail contains two curl feathers and one partially curled. 
August Ist, 1907.—Kclipse progressing very slowly ; the head 
is in much the same condition as it was when last noted. The 
breast has perceptibly lightened, light brown feathers barred with 
black alternating with the dark maroon feathers; a few typical 
eclipse feathers are coming through the down of the breast. 
The scapulars have somewhat darkened, and there are more 
barred feathers upon the flank, each showing up as blotched 
with dark, upon the grey vermiculated background of the older 
feathers. ‘These dark feathers appear to be new. ‘Tail as last 
deseribed. Although grey vermiculated feathers predominate 
upon the abdomen, they are intermixed with a number of 
brownish feathers with black centres: some of the latter are 
new; others are due to pigment changes. 
* On May 14th there were three curl feathers in the tail. 
