BRANCH CHORD AT A i CLASS PISCES: THE FISHES 277 



show a metamorphosis almost as striking as that of insects 

 or toads or frogs. 



Some fishes build nests. Sticklebacks build elaborate 

 nests in the brooks and defend them with spirit. Sun- 

 fishes do the same, but the nests are clumsier and not 

 so well cared for. 



The salmon is the type of fishes which run up from the 

 sea to lay their eggs in fresh water. The king salmon of 

 the Columbia River, for example, leaves the sea in the 

 high waters of March and ascends without feeding for over 

 a thousand miles, depositing its spawn in some small 

 brook in the fall. After making this long journey to lay 

 the eggs, the salmon become much exhausted, battered 

 and worn, and are often attacked by parasitic fungi. They 

 soon die, probably none ofthem ever surviving to lay eggs 

 a second time. 



Classification. A fish is an aquatic vertebrate, fitted 

 to breathe the air contained in water, and never develop- 

 ing fingers and toes. Accepting this broad general 

 definition we find at once that there are very great differ- 

 ences among fishes. Some differ more from others than 

 the ordinary forms differ from rabbits or birds. So 

 although we have entitled this chapter as if all fishes 

 belonged to the class Pisces, we cannot arrange them 

 satisfactorily in less than three classes. 



The lancelets (Leptocardii). The lowest class of fish- 

 like animals is that of the lancelets, the Leptocardii. 

 These little creatures, translucent, buried in the sand, of 

 the size and form of a small toothpick, are fishes reduced 

 to their lowest terms. They have the form, life, and ways 

 of a fish, but no differentiated skull, brain, heart, or eyes. 

 Moreover they have no limbs, no jaws, no teeth, no 

 scales. The few parts they do have are arranged as in a 

 fish, and they show something in common with the fish 



