354 



AVES. 



organ is either double, as in Serpents, when, 

 however, each penis is extremely small; or it 

 is single, but in this case, to whatever extent 

 it may be developed, it always consists of a 

 uniform ligamentous and vascular elastic sub- 

 stance, and, as in the Tortoise, is simply 

 grooved along the upper surface or dorsum for 

 the passage of the fecundating fluid. 



As there is no true urethral canal, so neither 

 are the glands of Cowper or the prostatic 

 glands present. 



The testes (x,fig. 166, Fig. 182. 



' . 182) are two in 



Fig. 183. 

 1. January. 



2. Middle of February. 



3. Beginning of March. 



y 



y- 



(i, a 



number; in form more or 

 less oval, situated above 

 the upper extremities of 

 the kidneys. They vary 

 remarkably in colour in 

 different birds; we may 

 mention, as examples, 

 that they are while in 

 the Peregrine Falcon and 

 and Dove ; pale yellow 

 in the Horn-Owl, and 

 Gallinule ; of a brighter 

 yellow in the Magpie, 

 Bay Ibis, Ruff, and Oys- 

 ter-catcher; of a black 

 colour in the Chough, 

 Partridge, Heron, Sea- 

 gull, but whitish towards 

 the lower end in the last 

 two. They are invested 

 with a strong and dense 

 albuginean tunic. Their 

 structure is evidently tu- 

 bular, the contorted tu- 

 bules are very slender, 

 scarcely exceeding in di- 

 ameter the seminal tu- Urinary and male organs 

 bules of mammalia : they f a Coch - 



are separated into packets by delicate and mem- 

 branous septa, continued from the inner surface 

 of the .tunica albuginea. 



The arteries spread in an arborescent form 

 beneath that capsule. The vas deferens (c c) 

 is continued from the posterior and internal 

 part of the gland. 



The periodical variations of size which the 

 testicles undergo are very remarkable in the 

 Class of Birds ; and the limited period during 

 which their function is in activity is compen- 

 sated by the frequency and energy with which 

 it is exercised. 



The proportional size which the testes ac- 

 quire at the breeding season is immense, as may 

 be seen in the subjoined figures (183) of the 

 testes of the House-Sparrow ;* which commences 

 with the glands as they appear in January, 

 when they are no bigger than pins' heads, and 

 ends with their full development in April. 



It rarely happens that both testes are deve- 

 loped in exactly the same degree, but the 

 increase of size is not limited to the one on 

 the left side. The right testis is as often the 



1 See John Hunter, in the Animal (Economy, 

 plate vii. 



4. Latter end of March. 



5. Middle of April. 



Testes of the House- Sparrow. 



largest, and we have seen an example, in a 

 Rook, where it alone had taken on the action 

 of sexual increase, and had acquired a bulk 

 compensating for the want of development in 

 the left testis. 



In most Birds, the only appearance of an 

 epididymis is a remnant of the Wolffian body 

 or primordial matrix of the genital and urinary 

 organs (b, Jig. 182). This part frequently pre- 

 sents a colour strikingly different from that 

 of the testes : thus it has been observed in 

 the Bustard and Curassow to be black ; in the 

 Cassowary, yellow ; and in the Anthropoides 

 Virgo to be of a green colour. 



In the Ostrich the epididymis is folded upon 

 itself at the side of the testis. 



The vas deferens commonly passes down 

 to the cloaca by the side of the ureters 

 without undergoing any remarkable convo- 

 lution ; but in the common Cock it is bent 

 upon itself in short transverse folds from side 

 to side almost from its commencement; the 

 folds gradually but slightly increase as they 

 approach the cloaca, both in extent and in the 

 diameter of the tube composing them, and 

 they are so closely compacted as to present in 

 a longitudinal section the appearance of a 

 series of cells, which are capable of retaining, 

 as in a vesicula seminalis, a quantity of the 

 seminal secretion. 



Each vas deferens in the Common Cock 

 terminates on a separate rudimentary penis or 

 papilla, situated in the urethro-sexual division 

 of the cloaca at a little distance from each 

 other, and anterior to, or sternad of the inser- 

 tions of the ureters. 



The base of each papilla is surrounded by a 



remarkable plexus of arteries and veins (M, M, 



Jig. 171) which serve as an erectile organ during 



the venereal orgasm, when the turgid papillae are 



