130 FISHES. 



the four gyrations of the valve are situated far hack towards 

 the end of the intestine. In Lcpidosteus the valve is rudi- 

 mentary, and indicated only by three raised lines crossing the 

 terminal portion of the intestine. In all these Ganoids the 

 rectum has a separate opening, without cloaca. 



The structure of the intestinal tract of Teleosteous fishes 

 is subject to so numerous modifications that we should go 

 beyond the limits of the present work if we would attempt 

 to enter into details. Great differences in this respect may 

 be found even in groups of the same natural families. 

 Frequently the intestinal tract remains of nearly the same 

 width throughout its course, and only the entrance of the 

 various ducts serves as a guide for the distinction of its 

 divisions. An intestine of such uniform width may be 

 straight and short, as in Scomhresocidce, Symhranchidce, or it 

 may be more or less convoluted and long, as in many 

 Cyprinidce, Doradina, etc. On the whole, carnivorous fishes 

 have a much shorter and simpler intestinal tract than 

 herbivorous. 



In the majority of Teleosteans, however, oesophagus, 

 stomach, duodenum, small intestine and rectum, can be more 

 or less distinctly, even externally distinguished. 



There are two predominant forms of the stomach, inter- 

 mediate forms being, however, numerous. In the first, the 

 siphonal, it presents the form of a bent tube or canal, one- 

 half of the horse-shoe being the cardiac, the other the pyloric 

 portion. In the second, the ccecal, the cardiac division is pro- 

 longed into a long descending blind sac, the cardiac and 

 pyloric openings of the stomach lying close together (Clupea, 

 Scomber, Thynnus, etc.) 



The duodenum receives always the hepatic and pancreatic 

 secretions, and, besides, those of the appendices pyloricee, 

 which, in varying numbers (from 1 to 200), are of very common 

 occurrence in Teleosteans (Fig. 56). They vary also in length 



