1844 THE STORY OF THE UNIVERSE 



liver, and other glands, s,erve for the digestion of the 

 food, and a heart and blood-vessels exist for the cir- 

 culation of the blood thus manufactured from the 

 food. The blood is purified in the gills. Each gill 

 consisting in common fishes of a supporting 

 "arch" bearing a great number of delicate filaments 

 arranged like the teeth of a comb may be viewed 

 as simply a network of blood-vessels. The blood, 

 pumped into this network by the heart, is purified 

 by the action of the oxygen gas contained in the pure 

 water which the fish is constantly taking into its gill- 

 chamber by its mouth; while the pure blood is re- 

 circulated through the body, and the water used in 

 breathing is got rid of by being ejected behind the 

 "gill-cover" at the neck, so as to allow a fresh inflow 

 to be drawn in by the mouth. The gills of some 

 fishes may be very differently constructed from those 

 of the common members of the class. Thus the lam- 

 preys breathe by pouch-like gills which open each 

 by a separate aperture. Seven gill-apertures may be 

 seen on each side of the neck of the common lam- 

 prey; and the sharks, skates, and their neighbors also 

 breathe by sac-like gills. Certain curious facts re- 

 garding the breathing of fishes will be afterward 

 alluded to. Fishes illustrate plainly what is meant 

 by aquatic or water-breathing. They possess gills 

 or organs, adapted for separating the atmospheric air 

 which is entangled or contained in the water; land- 

 animals breathing the same air directly from the 

 atmosphere. 



That fishes are wary and active, and possess senses 

 of acute nature, are facts well known to all. The 



