BIRDS. 349 



The male birds have two testes 1 which are placed upon the 

 anterior portion of the kidneys, on each side of the aorta and the 

 inferior cava. Their form is oval, the colour usually white or 

 yellowish. Commonly that of the left side is larger. During the 

 pairing season they increase greatly in size, whilst at other times 

 they are contracted into a small bulk 2 ; in birds living in polygamy 

 they are at all times larger than in others. A white and very 

 vascular membrane (tunica albuginea} covers the tissue of the testis, 

 which consists of many, very fine, convoluted tubules. These 

 tubules unite to form wider tubes, vasa efferentia; these afterwards 

 form the epidydimis which, scarcely distinct from the testis, lies as 

 an oval mass upon the tunica albuginea, and terminates below in 

 a point. From its extremity the very tortuous efferent vessel (vas 

 deferens) arises, which passing over the kidney and afterwards 

 along the outside of the ureter runs to the cloaca. In the develop- 

 ment of the two efferent vessels that difference is not remarked 

 which is often observed between the two testes. They become 

 wider in their course and in many birds expand at their extremity 

 into a vesicle (vesicula seminalis). The apertures of the two ef- 

 ferent vessels are situated externally to those of the ureters ; near 

 each of them is a small conical eminence which is highly vascular. 

 These two conical papillae are found in all birds ; they were for- 

 merly regarded, incorrectly, as a double penis. This organ is 

 wanting in most birds; only some possess a penis, without however 

 on that account being destitute of the aforesaid papilla?. The 

 penis which is met with in many waders (Ardea, Ciconia, Otis) 

 and in some gallinaceous birds (Crax, Penelope, Crypturus), is 

 only in a rudimentary state, of a tongue-shaped form, sometimes 

 with, sometimes without a conspicuous groove on its upper surface. 

 In the Anatince, in the genus Casuarius, and in the American 

 Ostrich, there is a penis which on copulation is in part brought 

 outwards by eversion, and which has on its internal surface a 



1 Some writers appear to have met with a single testis occasionally, or even with 

 three. 



3 ABISTOTELES De Animal. Hist. Lib. m. cap. i. This wonderful change in the 

 size of the testes from January to April has been represented by HUNTEB in the com- 

 mon sparrow (Fringilla domestica L.), Catalogue of the PJiysiol. Series, &c. Vol. IV. 

 Tab. 50, transferred by OWEN, TODD'S Cyclop. 1. 1. p. 354. 



