Ichthyopsida 



4.39 



cyclostome hag (Myxine) and the teleost "stargazer" (Astroscopus) . 

 Also the dipnoan has the '"lobe-fin'' characteristic of crossopterygians. 

 It seems likely, therefore, that the two groups were closely related at 

 their beginnings, since which the crossopterygians have become nearly 

 (or quite?) extinct and the dipnoans have been reduced to three sur- 

 viving genera. On the ground that the choanae of crossopterygians 

 imply possession of lungs, the Dipnoi and Crossopterygii may be in- 

 cluded together under the name Choanichthyes, a division of 

 Osteichthyes. 



Electric Organs 



Stories have been told of a curious mishap which may be suffered 

 by horseback riders while fording streams in Brazil or other tropical 

 parts of South America. For no obvious reason, the rider may be 

 plunged into the water by sudden panic or even collapse of the animal 

 under him. The cause of the mishap is mere contact with a harmless- 

 looking eel-like fish. But mere contact suffices to allow the fish to 



r io. ."539. Electric organs. (Left) Electric ray. Torpedo: dorsal view; electric 

 organs exposed by removal of skin and superficial tissue. (Right, above) Electric eel, 

 Electrophorus (Gymnotus): caudal location of electric organs indicated by solid black. 

 (Right, below) Stereogram showing relations of eel's electric organs to caudal mus- 

 cles and skeleton. (.4) Anus; (Au) Eye; (DM, DM 1 ) dorsal muscles; (E, E l ) electric 

 organs; (Ft) ventral fin; (//) skin; (K) gill-clefts; (LH) hemal canal; (S) cranium; 

 (Sep) connective-tissue septum; (Sp) spiracle; (VM, VM 1 ) ventral muscles; (WS, 

 WS l ) vertebral column. (Courtesy, Wiedersheim : "Grundriss der vergleichenden 

 Anatomie der Wirbeltiere," Jena, Gustav Fischer.) 



