CHAPTER XXVI 

 REPRODUCTION AND DEVELOPMENT OF ANIMALS 



346. Reproduction. In animals, as in plants, the func- 

 tion of reproduction is a function belonging to maturity. 

 The power of reproduction is not essential to the life of an 

 individual animal but is essential to the continuance of a 

 race of animals. 



347. Reproductive Organs. In the higher animals, as 

 in the higher plants, there are certain organs the function of 

 which is to provide for the making of other animals. These 

 organs are called reproductive organs. As in the higher 

 plants, these organs are of two kinds: one kind producing 

 inactive cells, called egg cells or eggs, such as are formed in 

 the ovule of the flower; the other kind producing very small 

 active cells, called sperm cells or sperms, such as are found in 

 the pollen grains of the stamen of a flower. Fertilization, 

 that is, the bringing together of the cells of the two kinds, is 

 generally necessary for the development of a new animal 

 organism. The number of eggs produced varies with different 

 animals, just as the number of seeds varies with different 

 plants. Insects and common fishes deposit many eggs at a 

 time; birds, a few. Some animals reproduce many times in 

 a season, some once a year, and some higher animals less 

 frequently. 



348. Sex. In animals, as in some plants, both kinds of 

 reproductive organs may exist in one individual organism, 

 but generally there is only one kind of organ in an individual. 

 Animals having only egg-producing organs, ovaries, are called 

 females ; those having only sperm-producing organs, sperma- 

 ries, are called males. With the egg cell, the female furnishes 



298 



