THE ANATOMY OF BIRDS. — OOLOGY. 
217 
The Kidneys (Lat. rcnes, Engl, reins, adj. renal; figs. 103, 104, a; 105, x) differ much 
from those of mammals in physical characters, though identical in function, — that of straining 
off from the hlood certain deleterious substances in the form of urea ; whence they are sometimes 
called emulgeni organs. Their office of purification is analogous to that of the lungs, which 
decarbonize the blood, and to some extent vicarious, as is that of excretory organs in general. 
As the lungs are closely bound dowm to the thoracic region of the trunk, so are the kidneys 
impacted in the pelvic region, being moulded to the sacral inequalities of surface (p. 141). 
They are paired, but sometimes connected across the median line by renal tissue ; they have no 
special renal artery, but derive their blood from various sources ; and blood from them takes 
part in the hepatic portal system, no reniportal being accomplished. They have little or noth- 
ing of the particular mammalian configuration which has made kidney-shaped " a common 
descriptive term ; being elongated, somewhat parallel -sided and rectangular, flattened bodies, 
lobated into a few large compartments, and lobulated into many lesser divisions ; their figure 
depends much upon that of the pelvis. They are very dark-colored, rather soft, easily lacerable, 
and appear to the naked eye to be of a granular substance, without dis- 
tinction of ''cortical" and ''medullary" portions. Nor is there any 
" pelvis" of the kidneys in which the uriniferous tubules empty together 
by numerous ducts as into a common basin. Each ureter (figs. 103, h ; 
104, e; 105, y), or excretory duct, is formed by reiterated reunion of the 
iubuli uriniferi, after the manner of a pancreatic duct ; each ureter passes 
down behind the rectum and opens into the lower back part of the cloaca, 
— much like a mammalian ureter into the base of the bladder. The 
original cavity of the allantois remains to furnish no more of a urinary 
bladder than some special dilatation of the cloaca represents ; but this 
rudimentary bladder, as distinguished from the uro-genital sinus in which 
the ureters terminate alongside the sperm-ducts, is well marked in some 
birds ) being in the ostrich, for example, a considerable enlargement of 
the cloaca between the termination of the rectum proper and the uro- 
genital compartment of the sewer. The renal excretion is not watery 
as in mammals, but semi-solid, and voided with the faeces, of which it 
forms part. 
The kidneys are capped by a pair of small yellowish bodies, the 
supra-renal capsules or adrenals (figs. 103, /; 104, 105, d), the nature 
of which is undetermined. They are chiefly interesting to the practical 
ornithologist in their liability to be mistaken for testes in examining Fig. 1C5. — Uro-gen- 
specimens for sex (see p. 45). ital organs of the domes- 
tic cock; after Owen. 
a, testis ; b, epididymis ; 
Male Organs of Generation.— The testis ■{\u'^iX. testis, -pi. testes, f^^ens'^^^'ad^enaT- "^t 
a witness; fig. 105, a) or testicle has been already sufficiently noticed as cloaca; x, kidney; y, 
to its general appearance and position (p. 46). As said above, it is the 
essential male organ, consisting of the primitive indifferent genital gland (fig. 103, e) in its 
highest state of development as a tubular secretory organ, connected with the remains of 
the wolffian body as a part of its efferent structure (epididymis; fig. 105, b) and with the 
original wolffian duct as its vas deferens (figs. 103, d; 105, c), or efferent duct, by which the 
semen is conveyed to the cloaca. The original glands normally remain paired, and both 
are usually functionally developed to corresponding size, shape, and activity ; they remain 
in their embryonic situation in front of the upper part of the kidneys ; and such difference 
semen from e, the testis. In fig. 104, 6 is the wolffian body, whose duct,/, disappears ; and g is the mullerian duct, 
becoming the oviduct, to convey the egg from c, the ovary. Thus e, fig. 103, and c, fig. 104, are the homologous 
genital glands, becoming either testis or ovary : but the sperm-duct, d, fig. 103, is not the oviduct, g, fig. 104. 
