^ LIVER OF FISHES. 425 



ancient Ganoids, like their modern representative, the Polypterus, 

 possessed the spiral valve. 



§ 73. Liver of Fishes. — The liver makes its first appearance 

 in the lowest vertcbrated, as in the lowest articulated, species, 

 under the form of a simple cajcal production from the common 

 alimentary canal. Commencing in the Lancelet, fig. 169, Jul, 

 a little beyond the orifice py, the hepatic CcGcum, /, extends 

 forward from its place of communication with the canal ii, and 

 terminates in a blind end. In the Myxinoids the liver, as in 

 all higher Fishes, fig. 282, «, is a well-defined conglomerate, or 

 acinous, parenchymatoid organ, with a portal and an arterial 

 circulation, with hepatic ducts, and generally a gall-bladder and 

 cystic duct, ib. c, by which the bile is conveyed to the duodenum, 

 from wliich the stomach is divided by a pyloric valvular ori- 

 fice. 1 



The texture of the liver is soft and lacerable ; its colour usually 

 lighter than in higher Vertebrates, being whitish in the Lophius, 

 and in many other Fishes of a yellowish grey or yellowish brown: 

 it is, however, reddish in the Bream, of a bright red in the 

 Holocentrum orientale, orange in Holocentrum hastatum, yellow in 

 Atherina ipreshyter, green in Petroniyzon marinus, reddish brown 

 in the Tunny, dark brown in the Lepidosiren, almost black in 

 the Paddle-fish. In the Sihtridm a portion of the liver, usually 

 forming a middle lobe, thinner than the rest and of a lighter 

 colour, has been described as the ' pancreas : ' it has a distinct 

 duct, opening near that of the ductus choledochus. In most Fishes 

 the liver is remarkable for the quantity of fine oil in its substance, 

 under which form almost the whole of the adipose matter is there 

 concentrated in the Cod tribe, the Eays, and the Sharks.^ Fishes 

 which, like the Salmon and Wolf-fish, have oil more diffused 

 through the body, have comparatively little oil in the liver. 



The liver is generally of large proportional size : it is attached at 

 the fore-part of the abdomen to the aponeurotic wall partitioning 

 off the pericardium, fig. 276, I, o, and extends backward, with a 

 few exceptions, further on the left than on the right side : in the 

 Carp, the Bream, and the Stickleback, the right lobe is longest. 

 Its shape varies with that of the body or of the abdominal cavity ; 

 it is broadest, for example, in the Kays, longest in the Eels ; not, 



' The Bream is the only fish in which I have found the cystic duct terminating 

 directly in the stomach. 



The myriads of Dog-fish captured and commonly rejected on our coasts sliow 

 that the fishermen have not yet taken full advaut.Tgc of this anatomical fact, which 

 exposes to them au abundant source of a pure and valuable oil. 



