IXTRODUCTION. 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 water, 

 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 tl^e 

 negroes have filled sometimes whole baskets during 

 the terrestrial excursions of the doras in search of 

 their natural element. 



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

 f Vide Naturalist's Library, Ichthyolog>% vol. 1. p. 72. 



