1004 



GENERATIVE APPARATUS OF BIRDS. 



2. Generative Organs of the Female. 



The development of the young animal taking place external to the female, 

 the generative organs are hmited to that producing the ovum, and the duct 

 through which it passes on leaving the ovary. 



Ovari/. — In birds there is only one ovary, which is situated on the left side, 

 the right one becoming atrophied very early in nearly all species. This ovary is 

 situated, hke the testicles, in the sublumbar region of the abdominal cavity, and 

 constitutes a more or less voluminous body, composed of a variable number of 



ova in process of development— some 



Fig. 541. 



OVAKY OF THE BIRD. 



a, c, c. Ova (eggs) in the various stages of develop- 

 ment ; 6, stieak without vessels, indicating the 

 point where the vesicle is about to rupture to 

 allow the ova to escape; d, ruptureil vesicle; 

 e, very small ovum showing tl^# cicatriculus. 



very young, little, and white ; others 

 more advanced in age, being larger and 

 yellow in colour. The ova are en- 

 veloped in a very vascular cellular 

 membrane, which, when they are ripe, 

 splits in a circular manner, following 

 an equatorial line, and permits the 

 escape of the essential part of the egg 

 — the i/elloiv (yolk), or vitellus. 



Oviduct. — This duct is long, very 

 wide and dilatable, and very flexuous. 

 It begins, near the ovary, by an un- 

 fringed pavilion, and terminates in the 

 cloaca by a somewhat narrow orifice, 

 which is considerably widened when 

 the Qgg passes through it.^ The egg 

 — composed, on entering the oviduct, 

 of the fundamental part named the 

 yolk, or vitellus— h enveloped in an 

 albuminous covering during its pro- 

 gress towards the cloaca, and after- 



wards with a protecting shell. The oviduct of birds is, therefore, something 

 more than an excretory canal, as it participates in the formation of the ovum. 

 It is composed of three membranes — an external serous, maintains the tortuous 

 tube ; a middle, muscular ; and an internal, mucous. 



In the two sexes, above the cloaca there is a diverticulum named the pouch 

 of Fabricius, which is extirpated in Brittany, in order to render the hen birds 

 sterile. 



• Instances of abdominal " egg-laying " have been observed. Reul gives examples in 

 which it was due to atresia of the oviduct {Annales de Med. Veterinaire de Bruxelles, 1887> 



