394 



ZOOLOGY 



SKCT. 



organ, to which the name bony labyrinth is applied. The tympanic 

 cavity and columella have the same arrangement as in the Lizard ; 

 the narrow Eustachian tubes open by a common aperture (Fig. 

 1051, eus. ap.) in the roof of the pharynx. 



Urinogenital Organs. The kidneys (Fig. 1051, kd, Figs. 1060 

 and 1061, k) have a very characteristic form. Each is a flattened 

 organ divided into three main lobes and fitted closely into the 

 hollows of the pelvis. It is formed from the metanephros, the 

 large mesonephros or Wolffian body, which forms the embryonic 

 kidney, undergoing atrophy. The ureters (ur.) are narrow tubes 



passing directly backwards to open into 

 the urodseum or middle compartment of 

 the cloaca. 



The testes (Figs. 1051 and 1060, is.) 

 are ovoid bodies, varying greatly in size 

 according to the season, attached by 

 peritoneum to the ventral surfaces of the 

 anterior ends of the kidneys. From the 

 inner border of each goes off a convoluted 

 vasdeferens (vd.), which passes backwards, 

 parallel with the ureter, to open into the 

 urodseum on the extremity of a small 

 papilla. The posterior end of the 

 spermiduct is slightly enlarged to form 



FIG. lo.")!). Columba livia. 7 7- / mi 



The right membranous laby- a vesiculct semmalis (v.s.). Ihere is no 



rinth, outer aspect. FA, am- copulatory organ. 



The female organs (Fig. 1061) are 



. 



anterior canal ; SB, anterior 

 canal. (From Wiedersheim, 

 after Hasse.) 



pulla of posterior canal ; 

 FB, posterior canal ; HA, 

 ampulla of horizontal canal ; i i i r 



HB, horizontal canal; lag. remarkable for the more or less complete 



atrophy of the right ovary and oviduct. 

 The left ovary (ov.) is a large organ in 

 the adult Bird, its surface studded with 

 follicles or ovisacs, varying in size from 

 about 15 mm. in diameter downwards, 



and each containing a single ovum. The left oviduct (1. od.} is 

 long and convoluted ; its anterior end is enlarged to form a wide 

 membranous ccelomic funnel (1. od."} into which the ripe ova 

 pass on their liberation from the ovisacs ; the rest of the tube 

 has thick muscular walls, lined with glandular epithelium, and 

 opens into the urodaeum. A fair-sized vestige of the right oviduct 

 (r. od.) is found in connection with the right side of the cloaca, 

 and a more or less extensive vestige of the right ovary is frequently 

 present. 



Internal impregnation takes place. As the ova or " yolks " 

 pass down the oviduct they are invested with the secretions of its 

 various glands ; first with layers of albumen or " white." next with 

 a parchment-like double shell membrane, and lastly with a white 

 calcareous shell. They are laid, two at a time, in a rough nest, 



