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GENERAL ZOOLOGY 



Fig. 186. — Head of the rattlesnake, based on a dissection to show the poison 

 apparatus, f, hollow fang, shown in vertical section, is hinged above to the 

 maxillary bone of the skull, so that it can be folded back when the mouth is 

 closed; p.s., poison sac, a modified salivary gland, whose duct conveys the 

 secretion to the fang; t, tongue, which is harmless and serves principally as a 

 tactile sense organ. As in the bee, the damage or injury is caused by the highly 

 toxic venom injected into the wound. 



Fig. 187. — Electric organs of Torpedo marmorata. A, dorsal view of entire 

 animal, the upper surface being partially dissected away to show the electric 

 organs, o, and the brain with its electric lobes, el, from which nerves pass to 

 the electric organs. B, Transverse section through the entire body at the level 

 of the electric lobes of the brain, showing the electric organs composed of flat 

 disks, electroplaxes, arranged in vertical columns. The polarity of the current 

 generated in the organ is indicated by plus and minus signs. (Redrawn from 

 Dahlgren, Carnegie Inst. Pub., after Fritsch.) 



