596 ORGANS OP SECRETION. 



salivation of food, and the development of salivary glands. 

 The imperfect aeration of their blood by means of this 

 aquatic respiration, is probably also connected with the pre- 

 ponderant development of their liver, that great emunctory, 

 supplemental to the lungs and branchiae in decarbonizing the 

 blood. 



The liver is large in fishes, as in mollusca, of a soft texture, 

 divided into numerous lobes, its tubuli are filled with a very 

 light coloured oily secretion, and there is generally a distinct 

 gall-bladder superadded to the ordinary biliferous cosca com- 

 posing the entire liver of invertebrata. The gall bladder is 

 sometimes wanting as in ammocetes, or a mere dilatation of 

 the hepatic duct as in petromyzon. The great size of the 

 gall-bladder and its constancy in this class, accord with the 

 carnivorous habits, and the consequent irregularity in the 

 supply of food, in most of the species, as seen also in the 

 reptiles and the predaceous tribes of other classes. As the 

 capillary blood-vessels furnish incessantly the materials of 

 the secretion, and the tubuli of the liver as constantly form 

 bile, the interruptions to the demand for that fluid, by the 

 irregular feeding of almost all carnivorous animals, necessi- 

 tate the development of a reservoir in the course of the 

 efferent duct, to prevent the bile from irritating the empty 

 intestine in time of fasting, and to afford a sufficient supply 

 for their excessive meals. In most herbivorous animals, with a 

 constant abundance of food, and an unceasing process of 

 digestion, no reservoir or gall-bladder is wanted, but rather 

 a constant and copious supply of bile direct from the tubuli 

 and ducts of the liver ; and thus the presence or absence of 

 this appendix, and its extent of development, are related 

 more or less obviously to the food and habits of animals. 



The liver of fishes is often disposed on the left side, or on 

 the median plain, or towards the right side of the abdomen, 

 being suspended by broad ligaments from the tendinous 

 diaphragm, and is generally deeply lobated, extending back- 

 wards, in front of the alimentary canal, as far as the pelvis, 

 and often partially enveloping the intestine as in the mollusca, 

 but without the central excavation often seen in the liver of in- 

 vertebrata. There are commonly one or more long hepatic ducts, 

 which unite with a long cystic duct from the large gall-bladder, 

 to form a short and wide common ductus choledochus which 

 opens into the commencement of the duodenum, immediately 



