226 



ZOOLOGY 



SECT. 



is so small that the bones are easily cut with a knife and weigh 

 astonishingly little when dry. 



Electric Organs. Three genera of Teleostomi possess electric 

 organs, the Electric Cat-fish (Malapterurus), one of the Siluridae, 

 found in the fresh waters of tropical Africa, the Electric Eel 

 (Gymnotus), a Physostome occurring in Brazil and the Guianas, 

 and an American Star-gazer of the genus Astroscopus. In Mala- 

 pterurus the electric organ extends over the whole body, beneath 



4 the skin ; in Gymno- 



tus (Fig. 901) there is 

 a pair of batteries in 

 the ventral half of the 

 greatly elongated tail ; 

 in Astroscopus the 

 electric organs are 

 situated on the upper 

 surface of the head 

 just behind the eyes. 

 As in the Elasmo- 

 branchs, the electric 

 organs are formed by 

 modification of muscu- 

 lar tissue. 



Digestive Organs. 

 Some Teleostomi are 

 toothless ; but in most 

 instances teeth are pre- 

 sent, and may be 

 developed on the pre- 

 maxilla, maxilla, pala- 

 tine, pterygoid, vorner, 

 parasphenoid, dentary, 

 basihyal, and bones of 



FIG. 901. Gymnotus electricus, A, showing the extent +!, kranpliial arr-Vioc 



of the electric organ (E). Fl, Central fin. B, small tne 



portion of tail, in section. DM. DM.' dorsal muscles ; Jt is characteristic of 

 E. E.' electric organ ; Fl, ventral fin ; H, skin ; LH, 



caudal canal ; Sep. fibrous septum ; VM. VM.' ventral most 



muscles ; WS, WS', vertebral column, with spinal j. -u _ 

 edersheim' m 



ws 



nerves. (From Wiedersheim's Comparative Anatomy.) 



m , . . , 



1 elCOStei, With 



ovno^fir>r. /-> f 

 eAuepuiuu 



Physostomi, that the 

 maxilla is edentulous and does not enter into the gape (Fig. 889). 

 In a large majority of species the teeth are small, conical, and 

 recurved, suitable for preventing the struggling prey from slipping 

 out of the mouth, but quite unfitted for either tearing or crushing. 

 In some Fishes, such as the Pike, the teeth are hinged backwards 

 so as to offer no resistance to the passage of the prey towards the 

 gullet, but effectually barring any movement in the other direction. 

 In many deep-sea Fishes (Fig. 894) the teeth are of immense size 

 and constitute a very formidable armature to the jaws. Many 



