272 



RESPIRATORY ORGANS OF FISHES. 



fluid, and then forces it through the apertures on each side of 

 the throat, into the gill-cavities ; and from these it passes out 

 by the other orifices just described. Fishes, in common with 

 other animals that breathe by gills, can only respire properly 



Fig. 155. LAMPREY. 



when these are kept moist, and are so spread out as to expose 

 their surface to the surrounding element. The act of respira- 

 tion can take place when they are exposed to air, provided 

 these conditions be fulfilled ; but in general it happens that, 

 when a Fish is taken out of water, its gills clog together and 

 dry up, so that the air cannot exert any action upon them ; 

 and the Fish actually dies of suffocation, under the very cir- 

 cumstances which are necessary to the life of an air-breathing 

 animal. 



318. There are certain Fishes, however, which are provided 

 with an apparatus for keeping the gills moist, somewhat re- 

 sembling that which has been already noticed in the land- 

 crab. The bones of the pharynx are extended and twisted 



in such a remarkable 

 manner (fig. 156), as 

 to form a number of 

 small cavities ; these 

 cavities the Fish can 

 fill with water; and 

 they form a reservoir 

 of fluid, from which 

 the gills may be sup- 

 plied with a sufficient 

 amount to keep them 

 moist during some 

 time. The gill-fila- 

 ments themselves are 



so arranged that they do not clog together ; and by this combi- 

 nation of contrivances, the species of Fish that are furnished 

 with it can live for a long time out of water, so as to be able to 

 journey for a considerable distance on land. Such a provision 



Fig. 156. RESPIRATORY APPARATUS OF ANABAS. 



