502 FISHES. 



auricle, and thence to the muscular ventricle. From the 

 ventricle it is driven up the ventral aorta, the base of which 

 forms a white non-contractile bulbus arteriosus. 



The ventral aorta gives off on each side four afferent 

 branchial vessels to the gills. Thence the blood is collected 

 by four efferent trunks, which unite on each side in an 

 epibranchial artery. The two epibranchials are united 

 posteriorly to form the dorsal aorta, while anteriorly they 

 give off the carotids which are united by a transverse vessel 

 closing the "cephalic circle." 



Blood enters the sinus venosus by two vertical precaval 

 veins, and by hepatics from the liver. Each precaval vein is 

 composed dorsally of a jugular from the head and a cardinal 

 from the body. The cardinals extend along the kidneys 

 and are continuous posteriorly with the caudal vein, but the 

 middle part of the left cardinal is obliterated. 



Excretory System. 



The kidneys are very long bodies, extending above the 

 swim bladder under the vertebral column. The argest 

 parts lie just in front of and just behind the swim bladder. 

 From the posterior part an unpaired ureter extends to 

 the urinary aperture, before reaching which it gives off a 

 small bilobed bladder. The pronephros degenerates ; the 

 functional kidney is a mesonephros. 



Reproductive System. 



The testes are long lobed organs, conspicuous in mature 

 males at the breeding season. The ovaries of the female 

 are more compact sacs, more restrictedly posterior in position. 



Two vasa deferentia combine in a single canal. The 

 likewise single oviduct is continuous with the cavity of the 

 ovaries. The genital aperture in either sex is in front of, 

 but very close to, that of the ureter. According to some 

 authorities the genital canals in Teleosteans are secondary 

 structures, unconnected with the archinephric or segmental 

 ducts, but the researches of Jungersen have made this very 

 doubtful. 



Development. 



The ova of the haddock, like those of other Teleosteans, 

 contain a considerable quantity of yolk, are fertilised after 



