THE ANATOMY OF BIRDS. — OOLOGY. 



223 



The Kidneys (Lat. renes, Engl, reitis, adj. renal; figs. 103, 104, a; 105, rr) 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 emidgent 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 down 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. 147). 

 They are paired, but sometimes connected across the median line by renal tissue ; they have no 

 special renal artery, but derive their blr)od from various sources ; and blood from them takes 

 part in the hepatic portal system, no reuiportal 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 laccrable, 

 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, b ; 

 10-t, e; 105, ?/), or excretory duct, is formed by reiterated reunion of the 

 iuhuli uriniferi, after the manner of a pancreatic duct ; each ureter passes 

 <l(>wn 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 urinar)/ 

 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 urn- 

 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 

 specimens for sex (see p. 40). 



Male Organs of Generation. — The testis CLvd. testis, Tp\. testes, 

 a witness; fig. 105, a) or testicle lias been already sufficiently noticed as 

 its general appearance and position (p. id) 



Fig. 105. — Uro-gen- 

 ital organs of the domes- 

 tic cock; after Owen, 

 a, testis; 6, epididymis; 

 c, sperm-duct or vas de- 

 ferens; (I, adrenal; k, 

 cloaca; x, kidney; y, 

 ureter. 



to Its general appearance and position (p. 4(5). As said above, it is the 

 essential male organ, consisting of the ]>rimitive indifferent genital gland (fig. 103, e) in its 

 highest state of development as a tubular secretory organ, connected with the remains of 

 the wfdffian body as a part of its efferent structure (epididymis ; fig. 105, b) and with the 

 original wolffian duct as its vas deferetis (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 101, h is the wolffian body, whose duct,/, disappears ; and g is the miillerlan duct, 

 becoming the oviduct, to convey the egg from c, the ovary. Thus <•, fig. 10.3, and c, fig. KH, are the homologous 

 genital glands, becoming either testis or ovary: but the sperm-duct, <1, fig. 103, is not the oviduct, </, tig. 104. 



