XII 



PHYLUM CHORDATA 



399 



electric Cat-fish (Malapterurus) and the electric eel (Gym- 

 notus]\ the former found in fresh waters of tropical Africa, and 

 the latter in Brazil and the Guyanas. 



Some Teleostomi are toothless, but in most instances teeth 

 are present, and may be developed, not only on pre-maxilla 

 and maxilla of the upper and the dentary of the lower jaw, 

 but on a number of other bones in the wall of the mouth and 

 pharynx. In most Teleostei the maxilla is devoid of teeth, and 

 does not enter into the upper boundary of the mouth opening. 

 In the great majority the teeth are small and very numerous, 

 adapted for preventing the 

 struggling prey from slip- 

 ping out of the mouth, 

 while quite unfitted for 

 either tearing or crushing; 

 but in many instances 

 teeth are comparatively 

 large and few in number, 

 and in some (Fig. 226) 

 there is a marked differen- 

 tiation of the teeth, those 

 in front of the jaws being 

 pointed or chisel-shaped, and adapted for seizing or cutting, 

 while the back teeth have rounded surfaces adapted for 

 crushing. The teeth may be either simply embedded in 

 mucous membrane so as to be detached when the bones 

 are macerated or boiled ; or they may be implanted in 

 sockets of the bone or ankylosed to it. Their succession 

 is perpetual, i.e., injured or worn-out teeth are replaced at 

 all ages. The Ganoids have a spiral valve in the intestine ; 

 this is absent in the Teleostei. Caeca (the pyloric cceca) are 

 commonly developed at the junction of the stomach and 

 small intestine. The anus is always distinct from, and in 



FIG. 226. Premaxillae of Sargus, showing 

 teeth. (After Owen.) 



