FEMALE ORGANS OF BIRDS. 



249 



127 



Eagle, Dove, &c., the number of enlarged ovarian ova or * yolks' 

 is correspondingly small ; but in tlie more prolific species, as the 

 Common Fowl, fig. 126, A, they are more numerous. The number 

 of young produced may be, by this means, in some degree in- 

 ferred, if the female of a rare species happen to be killed during 

 the breeding season. 



In the diagrammatic section of a full-sized ovarian ovum, B, fig. 

 126, o is the outstretched ovarian capsule and stroma forming the 

 ^ calyx,' p its peduncular connection with the rest of the ovarium ; 

 c is the common position of the germ-cell and discoid germ-yolk ; 

 ov, the two layers of the ovisac into which the blood-vessels 

 penetrate ; vm, the vitelline membrane. This membrane is 

 sufficiently strong and ductile to permit the ovarian ovum being 

 compressed into an elliptical form to 

 facilitate its passage through the con- 

 tracted part of the oviduct. Certain 

 changes now occur in the ovarian 

 ovum, and much addition is made to 

 it; but, before entering upon these, 

 the canal through which it passes and 

 in which the egg is completed must be 

 described. 



In the female embryo the basis or 

 stroma of the ovarium, fig. 127, c, ap- 

 pears in a similar relation to the pri- 

 mordial kidneys (ib. b), as the testis 

 in the male. At the period when the 

 permanent kidneys, ib. a, have sent 

 the ureters, ib. e, to the cloaca, the 

 oviducts, g, have been developed as 

 prolongations from that part, and, to a 

 certain point of developement, they are 

 of equal size and length. Subse- 

 quently the left oviduct alone proceeds to grow ; the right is 

 stationary, or shrivels : occasionally it may be discerned as a 

 rudiment in the mature bird, but usually all trace of it has dis- 

 appeared. The left oviduct expands above or at its free end into 

 the infundibular orifice, fig. 125, b, where its parietes are very thin ; 

 as it descends, these increase in thickness, and the efferent tube 

 gradually acquires the texture and form of an intestine. Like 

 this, it is attached to and supported by a duplicature of peritoneum 

 called the mesometrium, but which also includes muscular fibres, 

 to be presently described. 



Kidneys, 'Wolfflan bodies, ovaries, and 

 oviducts of a foetal bird, at a period 

 wlien botli oviducts are still of nearly 

 equal size. Magnified, lxxiv. 



