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AN INTRODUCTION TO ZOOLOGY. 



rounded skull, as in the higher vertebrates. In the 

 frog's skull, too, it may be clearly distinguished that 

 the membrane bones are applied outside the cartilage 

 bones ; but in the higher vertebrates this is not so, 

 and the membrane bones can only be distinguished 

 from the others by tracing their existence throughout 

 the vertebrate series. 



Pig. 96.— The Electric Ray (Torpedo), under side. The spotted areas indicate 

 the place of the electric organs. 



Electric Fishes.— One of the most curious and 

 important facts to be recorded in connection with 

 Fishes is the existence, in some fishes, of electric 

 organs. These fishes belong to difierent groups, the 

 Torpedo, or Electric Eay, being one of the Selachii, 

 while the Gijmnotus, or Electric Eel of South America, 



