FISHES DIAGRAM 5 95 



CLASS OF FISHES. 

 DIAGKAM 5. 



Fish are cold-blooded animals like reptiles, but they always 

 live in water, and breathe by means of gills. They are shaped 

 liked combs, and are of a fine red colour, as may be seen on rais- 

 ing the gill-covers. Fish breathe by taking in water by the 

 mouth, and discharging it through the gills. On touching the 

 gills, the air which is contained in the water, parts with its 

 oxygen, and takes up in exchange carbonic acid from the blood, 

 so that the respiration of fishes does not differ essentially from 

 that of mammals and birds ; only it is effected by means of the 

 air contained in the water, instead of atmospheric air. 



The limbs of fish are replaced by fins ; but they swim in the 

 water, especially when they wish to move quickly, by the motion 

 of the tail alone. Many have a bladder in the body, which is 

 completely closed and filled with air to assist them to float in 

 the water. Most fish are very voracious, and swallow their prey 

 at a single gulp. 



They lay a great many eggs, but often very small ones ; and 

 when the animal is full of eggs, it is said to be full of roe, which 

 is the name generally applied to fishes' eggs. It has been 

 estimated that a salmon may lay 27,000 eggs ; a pike 500,000 ; 

 a sole, 100,000; a mackerel, 500,000; and a cod-fish from 3 to 

 9 millions of eggs. 



