242 ANATOMY OF VERTEBRATES. 



CHAPTER XXIII. 



GENERATIVE SYSTEM OF BIRDS. 



§ 167. Male Organs and Semination. — The few varieties of 

 structure wliicli the generative organs present in the Class of 

 Birds, are principally met with in those of the male. 



The organs in this sex exhibit all the essential characteristics 

 of the oviparous type of structure. The testes are situated high 

 up in the abdomen, whence they never descend into an external 

 scrotum. The intromittent 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 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, figs. 89, x, Wl ,a, a, are two in number ; in form more 

 or less oval, situated near the upper extremities of the kidneys. 

 They vary remarkably in colour in different birds ; I have seen 

 them white in the Peregrine Falcon and Dove ; pale yellow in the 

 Horn-Owl and Gallinule ; of a brighter yellow in the Magpie, 

 Bay Ibis, Buff, and Oyster-catcher; of a black colour in the 

 Chough, Partridge, Heron, Seagull, but whitish toward the 

 lower end in the last two. They are invested with a strong and 

 dense ^ albuginean ' tunic, and are fastened or suspended by a fold of 

 peritoneum. The contorted seminiferous tubules are very slender, 

 and are separated into packets by delicate and membranous septa, 

 continued from the inner surface of the tunica albuginea. The 

 arteries spread in an arborescent form beneath that capsule. The 

 vas deferens, fig. 117, c, c, is continued from the posterior or 

 ^ dorsal ' and internal or ^ mesial ' 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 compensated by the 

 frequency and energy with which it is exercised. 



The proportional size which the testes acquire at the breeding 

 season is immense, as may be seen in the subjoined figures of the 



