‘¢ RCLIPSE” PLUMAGE IN THE MALLARD. Did 
July 4th. Bird in almost full eclipse. 
Testes oval, about 6 mm. in transverse diameter, pale yellow in colour, and 
firm on section. Tubuli small with well-defined lumen. Cells for the most 
part two deep. No spermatogenesis. 
July 8th. Full eclipse. 
Testes small, scarcely 10 mm. long by 5 mm. broad. Tubuli of compara- 
tively small size, furnished with well-developed lumen. Cells two and three 
deep. No spermatozoa. 
July 12th. Full eclipse. 
Testes about 20 mm. long by 12 mm. broad; weight of each gland about 
3700 mg. Tubuli of fairly large size, no lumen. Cells in the centre of the 
tubuli are small. Here and there the sheaf arrangement of spermatids is 
indicated, but the nuclei are mostly badly stained. No properly stained 
spermatozoa, 
July 12th. Full eclipse. 
Testes resemble those of preceding ; no spermatozoa to be seen. Weight 
of testes together, 6560 mg. 
August 17th. Full eclipse. 
Testes small, diameter of transverse section 4mm. Tubuli small, stroma 
relatively large in amount. Tubuli furnished with well-defined lumen, cells 
about two deep. No spermatogenesis. 
August 21st. Hclupse. 
Testes small, about 5 mm. in transverse diameter. Tubuli narrow, quite 
inactive. A single layer of peripheral cells; a narrow lumen; no trace of 
spermatozoa. 
September 14th. Eclipse passing off. 
Testes about 7 mm. in transverse section; weight 195 mg. Tubuli of 
small size, with a narrow central lumen lined with one or two layers of cells ; 
no signs of spermatogenesis. 
(In a bird killed September 13th, the testes were 6 mm. in transverse 
diameter ; the tubuli of fair size, and filled with loosely aggregated cells; no 
spermatogenesis.) 
September 30th. Eclipse passing off. 
Many young feathers of winter plumage coming through on 
breast and abdomen. 
Testes small, firm, somewhat brown, about 12 mm. long and 3 mm. broad. 
Tubuli of medium size, with central lumen ; lined with cells averaging two 
deep. 
September 30th. Full winter plumage. 
Testes small, firm and somewhat brown, about 12 mm. long, but scarcely 
3mm. broad. The tubuli are of medium size only, and are filled with cells. 
October 9th. Full winter plumage. 
Tubuli of medium size and filled with cells. Spermatogenesis is not in 
progress, but amidst the central cells there appear here and there a few rod- 
