386 



COMPARATIVE SPLANCHNOLOGY. 



tissue. They present several openings on their surfaces, which communicate 

 with air-sacs hollowed out in the cellular tissue of the body. These sacs are 

 continuous with the interior of certain "bones, which thus receive a constant 

 supply of air (see p. 119). There are usually nine sacs — viz., one inter- 

 claviciolar, and the cervical, anterior and 

 lateral thoracic, and abdominal, which are 

 pairs. By means of these, air penetrates 

 nearly every region of the body. 



The kidney is very irregular in shape, con- 

 sisting of several portions which occupy the 

 osseous irregularities in the sublumbar and 

 anterior pelvic regions. The ureters open into 

 the cloaca, a diverticulum of which is regarded 

 as the analogue of the urinary bladder ; the 

 latter organ is distinctly possessed by only 

 one member of the class, the ostrich. 



The testicle is abdominal, occupying almost 

 the position of the mammalian kidney, which 

 it resembles somewhat in shape, being ovoid. 

 There is scarcely any epididymis ; the vas 

 deferens is tortuous, and it terminates in the 

 cloaca at the side of a papilla, which is the 

 organ of copulation. In the natatores this 

 papilla is very large, spirally elongated, and 

 retractile. 



In the bird there is only one ovary, the 



right one being undeveloped. It resembles 



a bunch of grapes in form, consisting of ova 



in various stages of development ; the more 



advanced ones are large, and yellow in colour. 



The representative of the Fallopian tube is 



called the oviduct, which is large, flexuous, 



and very dilatable, leading to the cloaca. It 



is not merely the duct of the ovary, since it 



also assists in forming the ovum ; while the 



latter is passing through it, the outer casL;3g of 



calcareous material known as the shell, and the inner layer of albumen or 



*' white of the egg" become developed. The coats of the duct are seroua, 



anuscular, and mucous, arranged in the typical manne?;. 



Fio. 149. 



TJrino-genital organs, &c., of a 

 male bird (fowl). 1, Heart ; 2, (Eso- 

 phagus cut across ; 3, Aorta ; 4, Pos- 

 terior cava ; 5 5, Psoe muscles ;' 

 n o, Testicles ; 6 6, Vasa deferentia ; 

 i'b', their orifices; ce. Suprarenal 

 capsules; drf, Kidneys; e«, Ureters; 

 e' €, Their openings into the cloaca. 



