CIRCULATORY SYSTEM OF THE HADDOCK. 437 



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." 



Just before the epibranchials unite to form the dorsal aorta, each gives 

 off a subclavian to the pectoral fin. The cceliac and the mesenteric 

 arteries arise from the right epibranchial in front of the subclavian. From 

 the ventral region of the first efferent trunk, a hyoidean artery arises ; it 

 gives off a branch to the pseudobranch, and another to join the epi- 

 branchials. Blood leaves the pseudobranch by an ophthalmic artery, 

 which is connected with its fellow on the opposite side, but is continued 

 forwards to the choroid of the eye. From the combined bases of the 

 hyoidean, and the two first efferent branchials, an artery is given off 

 on each side ventrally ; the two unite in a median vessel which supplies 

 pericardium, heart, and pelvic fins. 



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 largest 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 meso- 

 nephros. 



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 



