206 BRANCH CHORDATA 



the mountain streams, while the catfish can live in exceedingly 

 warm water. "Fishes have been found in hot springs of 120° F." 

 The Protop'terus of Africa and Asia "so completely slimes a ball 

 of mud around it that it may live thus for more than one season."^ 

 Other fishes bury themselves in the mud and cestivate through 

 the dry season. The little "mud-skippers" move from pond to 

 pond by the use of their pectoral fins. Other fishes migrate to 

 cooler waters as necessity requires. In winter some of the 

 fishes of our small streams hibernate in the mud, while some, 

 as the carp, may have the water frozen into ice about them and 

 live when thawed out. 



Development. — The sexes are separate. Multiplication is 

 by eggs, which are numerous. The cod is said to lay one 

 million eggs. In the bony fishes the eggs are naked and numer- 

 ous, and fertilization usually takes place in the water. 



In sharks the eggs are few and are protected by a horny shell. 

 In most sharks and in a few bony fishes the eggs are fertilized 

 and hatched within the body of the mother fish. Mating takes 

 place in a few viviparous forms only. Most fishes do not care 

 for their young "fry," but the stickleback builds a nest and de- 

 fends it with great courage. There is usually no metamorphosis, 

 but some ocean species change almost as much as frogs. 



SUB-CLASS I. ELASMOBRAN'CHII 



The rays and sharks represent the Sela'chil, in which are found 

 all the living elasmobranchs. They have no operculum (gill- 

 cover) and no air-bladder. The skeleton is cartilaginous. The 

 mouth and nostrils are ventral and the tail heterocercal.^ 

 The scales are small. "The cloaca is the common outlet for the 

 rectum, renal and reproductive ducts." Some are viviparous, 

 others lay a few eggs, each enclosed in a chitinous case. 



Sharks vary in length from 2 to 60 feet, the majority being 

 under 8 feet in length. Some are large and voracious, a few 

 dangerous even to man. Hornaday says the only loss of life 

 from sharks on our coast occurred in 1830. They feed mostly 

 upon fishes. 



The rays (Rai'idoe) have the body disk shaped, broad, and flat, 



1 Baekett. 2 Glossary. 



