INTRODUCTION. 113 



waters, upwards of one thousand pacou, and the 

 fry of other kinds of fish to a finger s length ; but 

 in all this wholesale destruction, I have never seen 

 a pacou less than a foot long." * There is no doubt 

 that the fish does not descend the rivers till of a 

 sufficient age and strength to venture among the 

 turbulent waters at the cataracts, where its favourite 

 food, the waia^ is growing. 



A species of fish, which belongs to the same 

 division as the callichthys^ namely the Doras Han- 

 cockii of Cuvier and Valenciennes, possesses the 

 singular property, as we are told already by Mar- 

 grave of his Tamoata^ of travelling over land. I 

 have been informed by eye-witnesses, that they 

 have met sometimes whole droves during the dry 

 season, when those pools of water which had re- 

 mained from the last inundation were about to dry 

 up. They then march over land in search of w^ater, 

 and the shields with which their body is armed, as 

 well as the strong spring ray of their pectoral fins, 

 serve to help them forward. It is thought that 

 " they have the power of retaining a portion of 

 water in a membranaceous bag surrounding the gills, 

 which keeps the filamentous structure moist, and 

 enables the animal to continue the respiratory ac- 

 tion." t So numerous are those droves, that the 

 negroes have filled sometimes whole baskets during 

 the terrestrial excursions of the doras in search of 

 their natural element. 



* Journal of the Royal Geograpliical Society, vol. iv, p. 33. 

 t Vide Naturalist's Library, Ichthyology, vol. i. p. 72. 



H 



