VENOMS IN THE ANIMAL SERIES 



305 



most curious genus among the fishes belonging to this family is 

 Holacanthus, in which the praeoperculum is provided with an 

 enormous spine like that of the Weever. Holocanthiis imperator 

 (fig. 114) is met with fairly often in the Indian Ocean and Malay 

 Archipelago. 



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Fig. 114. — Holacanthus imperator (Indian Ocean and Malay Archipelago), 



(After Savtschenko.) 



B. — Teleostei. — Plectognathi. 



The Order Plectognatlii (Family Gymnodontes) includes the 

 genera Diodon, Tetrodon and Triodon, globular fishes, in which 

 the jaw is transformed into a beak and furnished with a sharp 

 dentary plate. Their oesophagus is dilated into a resonant air- 

 pouch. When removed from the water they swallow air and 

 dilate the pouch, and the expulsion of this air is accompanied 

 by a loud noise. 



Several species of Tetrodon are armed with spines, which pro- 

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