214 INTRODUCTION TO ZOOLOGY. 



capable of bearing considerable extremes of heat and cold. 

 The delicate-looking Gold-fish thrives and breeds to excess in 

 water the temperature of which is so high as 80, and has 

 been known to be frozen into a solid body of ice, and revived 

 by the gradual application of warmth.* 



FORM. The great variety of form observable among fishes 

 may be illustrated by reference to some of our most common 

 native species the Eel, the Plaice, and the Haddock. Some 

 fishes have aspects so strange and grotesque that the names 

 -Fiddle-fish," "Red-riband," and "Hammer-head," have 

 been bestowed on them, as indicating their resemblance to 

 some well-known object. There are some which, to a certain 

 extent, can vary the form of their body at pleasure. Thus 

 the Diodon,t or Globe-fish (Fig. 179), by swallowing air, 



Fig. 179. GLOBE-FISH. 



can inflate itself like a balloon. The air passes into the first 

 stomach, which occupies the lower surface of the body. This 

 part, becoming the lightest, is that which remains uppermost, 

 and the fish floats on the surface with its usual position re- 

 versed. But, while thus floating without effort, it is in the 

 most perfect security from all its usual enemies ; for, owing to 

 the distension of the skin, the numerous spines with which it 

 is beset become erect, and present a bristling front on every 



* Jesse's Second Series of Gleanings in Natural History. 



f This fish belongs to a family which has no true teeth, but in which 

 the gums are covered with a substance resembling ivory. The enamel in 

 each jaw is without any division, so that the fish appears to have but two 

 teeth whence its name Diodon. 



