SEC. VIII MISCELLANEOUS PARTICULARS 69 



the barnyard cock and hen, for instance, yet the outward character- 

 istics are more frequently obscure, if not altogether inappreciable, 

 on examination of the skin alone. Young birds, moreover, are 

 usually indistinguishable as to sex, although the adults of the same 

 species may be easily recognised. The rule results, that the sexual 

 organs should be examined as the only infallible indices. The 

 essential organs of masculinity are the testicles ; similarly, the ovaries 

 contain the essence of the female nature. However similar the 

 accessory sexual structures may be, the testicles and ovaries are 

 always distinct. The male organs of birds never leave the cavity 

 of the belly to fill an external bag of skin (scrotum) as they do 

 among mammals ; they remain within the abdomen, and lie in the 

 same position as the ovaries of the female. Both these organs are 

 situated in the belly opposite the " small of the back," bound 

 closely to the spine, resting on the front of the kidneys near their 

 fore end. The testicles are a pair of subspherical or rather ellip- 

 soidal bodies, usually of the same size, shape, and colour, and are 

 commonly of a dull opaque whitish tint. They always lie close 

 together. A remarkable fact connected with them is, that they are 

 not always of the same size in the same bird, being subject to 

 periodical enlargement during the breeding season, and corresponding 

 atrophy at other seasons. Thus the testicles of a house sparrow, 

 no bigger than a pin's head in winter, swell to the size of peas in 

 April. The ovary (for although this organ is paired originally, only 

 one is usually functionally developed in birds) will be recognised as a 

 flattish mass of irregular contour, and usually whitish colour ; when 

 inactive, it simply appears of finely granular structure which may 

 require a hand lens to be made out ; when producing eggs, its 

 appearance is unmistakable. Both testis and ovary may further be 

 recognised by a thread leading to the end of the lower bowel, — in 

 one case the sperm-duct, in the other the oviduct ; the latter is 

 usually much the more conspicuous, as it at times transmits the 

 perfect egg. There is no difiiculty in reaching the site of these 

 organs. Lay the bird on the left side, its belly toward you : cut 

 with the scissors through the belly-walls diagonally from anus to 

 the root of the last rib, or further, snipping across a few of the lower 

 ribs, if these continue far down, as they do in a loon, for instance. 

 Press the whole mass of intestines aside collectively, and you at 

 once see to the small of the back. There you observe the kidneys, 

 — large, lobular, dark reddish masses moulded into the concavity 

 of the sacrum (or back middle bone of the pelvis) ; and on their 

 surface, toward their fore end, lie testes or ovary, as just described. 

 The only precaution required is, not to mistake for testicles a pair 

 of small bodies capping the kidneys. These are the adrenals or 

 suprarenal capsules, — organs whose function is unknown, but 



