18 RESPIRATION AND HEAT OF FISHES. 



water placed above their gills. These reservoirs, situated under 

 the operculum, and formed by the plates of the pharyngeal 

 bones, effectually serve to retain a certain quantity of water, 

 which keeps the gills moist when the animal is in the air, and 

 enables it to live there for some time : hence these fish are 

 accustomed to leave the rivers and ponds, which are their usual 

 abode, and convey themselves to considerable distances by 

 crawling in the grass or on the ground. Those which present 

 this labyrinthiform apparatus in its highest degree of complica- 

 tion, and which have received the name of Anabas, not only 



FIG. 261. ANABAS. 



remain very long out of the water, but can even, we are told, 

 climb up trees. The greater part of the fishes of this family 

 inhabit India, China, and the Moluccas. One species, the 

 Gourami, which originally belonged to China, and which is 

 much esteemed for its savoury flesh, has been naturalised in the 

 ponds of the Isle of France and of Cayenne. 



539. As already stated, Fishes produce scarcely any heat ; 

 that is, their temperature is usually but little above that of the 

 medium they inhabit. The Tunny, Sword-fish, and their 

 allies, however, constitute an exception to this rule ; for they 

 are able to sustain a fixed temperature of about 90 ; and they 

 are distinguished from other Fishes by the greater redness of 

 their blood, which results from the larger proportion of red 

 corpuscles. Several of this class have the singular power of 

 developing Electricity, and of giving very strong shocks to the 

 animals which touch them. The Torpedo, the Silurus or 

 Malapterurus, and a species of Gymnotus, are thus constituted; 

 and it is a remarkable thing that the electrical organ presents a 

 very different conformation in each of them. 



