lvi INTESTINAL TRACT. 



placed. In the amphioxus the isolated bodies which are seen near the 

 abdominal pore have been considered as the kidneys. 



LARGE ABDOMINAL GLANDS. 



The liver generally occupies a large portion of the abdominal cavity, 

 being separated from the cardiac chamber by a species of membranous 

 diaphragm. It is most developed among the plagiostornes, and as a rule 

 contains a large amount of oil. Its form is subject to considerable variation, 

 but it is generally tabulated, the most simple being found in the amphioxus as 

 a diverticulum from the stomachic dilatation of the intestinal tract. As a 

 rule a gall-bladder exists, and although it is generally seen at its lower 

 surface, it -may be lodged inside the liver near its centre, attached to the 

 r ight lobe, or even be distinct from this organ, being merely connected to it 

 by the cystic duct. Bile is removed from the liver by one or more ducts, 

 which converge into and join the cystic duct, thus forming the ductus 

 choledochus or common duct of the liver and gall-bladder, which empties 

 itself into the intestinal canal, posterior to the pyloric end of the stomach, 

 while in the plagiostomes it opens in the duodenum. 



A pancreas, as already observed, is found in many teleosteans, in the 

 sturgeon, and among the plagiostomes. 



The spleen among fishes is found, except in the amphioxus, as a dull 

 reddish body of a rounded form, usually placed near the stomach or 

 commeucement of the intestines. It is subject to considerable modifications. 



BREEDING. 



Fishes are dioecious, and although hermaphrodites have been observed 

 in a few teleostean forms,* the sexes are as a rule normally present in 

 different ' individuals. Some are monogamous, as the snake-headed- and 

 tropical Ophiocejjhalus, perhaps also our common pike, and many others. 

 The majority, however, are polygamous, or perhaps mixogamous, in which 

 latter the males and females congregate for breeding purposes, those of the 

 former sex being in excess, and several attending on one female, or even 

 changing about to another. 



Among most of the cartilaginous fishes, Gliondropterygii, of the order 

 Elasmobranchs, as sharks, rays, and skates, a congress takes place between 

 the two sexes, the arrangement of the sexual organs being somewhat similar 

 to what obtains among the higher vertebrates. The male organs are mostly 



* Hermaphrodites have been recorded among the following British fishes : Perca fluviatilis, 

 S^rranus cabrilla, Scomber scomber, Labrus mixtus, Solea vulgaris, Gadus morhua, 0. merlangus, 

 Lota vulgaris, Esox lucius, Cyprinus carpio, Clupiea liarengus, Acipenser sturio. 



