257 
Palmipedes especially, where they are of larger size, they extend 
more forwards ; and in many of the Accipitrine birds they are placed 
more upon the fatty prominence which supports the quill-feathers. 
In the Scolopacide and Columbide they are seated between the two . 
central tail-feathers. 
Structure.—Externally the gland is covered with a fibrous capsule, 
which is extremely vascular. I have failed at present to inject the 
interior of the glandular structure, nor have I succeeded in tracing 
nerves into it. In many birds, however, when examined soon after 
death, the blood-vessels may be seen running in parallel lines with 
the tubules, and ramifying upon them. The glands are generally 
thinly covered with short supple feathers of a downy character, and 
their flask-like necks are usually surmounted by a tuft of short soft 
feathers, varying greatly in number in the different orders, but more 
abundant in the swimming birds. In the Pelicanide these tufts are 
very large, and will hold a great quantity of oil. In other birds, as 
in the Columbide, the ducts are quite bare of feathers. 
In the centre of each nipple, which is generally encircled by fea- 
thers, is a round, smooth, single orifice, through which a probe can 
be readily introduced, and through which aperture the fluid contents 
of the glands; especially in the living birds, can easily be squeezed 
out. The two glands are closely united at their posterior part by 
dense fibrous tissue. The internal portion of the gland consists of 
elongated cylindrical glandules or tubules, as described by Prof. 
Owen, which supply the secretion. They pass generally from before 
backwards, taking an oblique longitudinal direction, and they termi- 
nate im rounded extremities, having, I think, a small central aperture ; 
but of this I speak with some amount of hesitation. These tubules 
resemble somewhat the proventricular glandules. In some diseased 
glands the contents of the tubules are readily seen under a low 
power, and if immersed for some time in ether, and then dried, they 
are more distinctly visible. They all terrinate in what may be called 
the cavity of the gland, a small space varying in size in different 
birds, and generally partly filled with the fatty or oleaginous secre- 
tion, but sometimes found quite empty. In some birds this por- 
tion of the gland is interlaced with a network of fibrous tissue, in 
which the segretion is partly lodged. 
In young birds; as shown by the Thrushes on the table, the glands 
are small, semitransparent, gelatinous, and very vascular under a low 
power, and an abundant network of vessels is seen to ramify on the 
surface; the brush or tuft is indicated by a minute black speck, as 
are also the duct-orifices. I think I have found the glands larger and 
more perfect at birth in feathered birds, as in the Duck and Plover; 
but my observations are not sufficiently numerous to enable me to 
speak with certainty on this point. 
Nature of the secretion.— It varies much in consistence, sometimes 
being thick and pap-like, and at other times clear like pure oil. It 
leaves a greasy stain upon blotting-paper, burns after a time with 
a brisk flame, dissolves readily in ether, and forms an oily, soapy 
compound with potash. Under the microscope it presents various 
No. 433.—PrRocEEDINGS OF THE ZOOLOGICAL SOCIETY. 
