10 COJIPAEISONS OF STRUCTURE IK ANIMALS, 



sole — others, again, are elongated and somewhat 

 snake-like, as the eel. 



Most fishes are covered with scales, arranged 

 in regular order ; in some species, however, 

 they are so minute, that, in a popular sense, 

 the fish may be called naked, as, for example, 

 the eel. In several species the skia is rough, 

 being minutely granulated with hard tubercles. 

 Some, as the pipe-fish and hippocampus, are 

 invested with a sort of armour of indurated or 

 horny plates ; while in others, as the ostracion, 

 these plates are so consoHdated as to form a 

 sort of bony box, the tail, the fins, and the 

 mouth being alone movable. 



It is not only by scales, or other appendages, 

 that the skin of fishes is defended from the 

 action of the water in which they dwell — they 

 are externally lubricated by a tenacious shme 

 the secretion of certain glandular pores, whence 

 it exudes abimdantly. Most fishes produce 

 eggs in vast numbers, collectively termed the 

 roe; but some of the sharks are viviparous, 

 and so is the angel-fish, (^Squatina angelus.) 

 This observation applies to reptiles, these 

 animals being, as a rule, oviparous, with the 

 exception of a few lizards, and certain venomous 

 snakes, which produce living young. 



