THE FIVE CLASSES OF VERTEBRATES. 123 



The organ of smell appears to be well developed, the 

 olfactory nerve being large, and sending off branches to 

 the nasal sacs, little blind sacs in the nasal fossae. 



The touch is exercised by the barbels or lips. 



There appears to be no sense of taste. 



Eeproduction takes place by eggs. The fecundity of 

 the carp, like that of many other fishes, is so great that 

 it has become proverbial. A female carp of good size 

 contains not less than five or six hundred thousand eggs. 

 These eggs are deposited on the leaves of aqueous plants 

 in March or April, and hatch in seven or eight days. 

 The growth of the young is very rapid ; if the conditions 

 are favorable a young carp attains in three years' growth 

 a weight of five or six pounds ; afterwards the growth 

 is much slower. 



Carp flourish in ponds as well as in rivers whose cur- 

 rents are slow. They feed on larvae, worms, grain, aquatic 

 herbs, and young vegetable sprouts ; often, indeed, they 

 rise and seize insects on the surface of the water. 



CHAPTER XII. 



Review of the Distinguishing- Features of the Five 

 Classes of Vertebrates. 



IN the preceding chapters we have taken one example 

 from each of the five classes of the great group of ver- 

 tebrates. We have seen the differences that distinguish 

 the mammalian dog from the chicken, and have studied 

 the peculiarities in structure of reptiles, batrachians, 



