216 



EXPERIMENTAL GENERAL SCIENCE 



183. Reproduction. All living things must reproduce them- 

 selves, else their particular forms would soon cease to exist. 

 In the simplest kinds, reproduction consists in the dividing 

 of the cell into two equal parts each of which grows up and 

 becomes a new individual. In higher forms, reproduction is 

 a function of certain cells set apart for the purpose. These 

 may divide into a number of small bits called spores, each of 

 which is capable of producing a new individual, or they may 

 form similar bodies which are unable to produce new indi- 

 viduals without uniting in pairs. Such uniting bodies are 

 called gametes. In all the higher 

 animals and plants, reproduction is 

 by the union of gametes. When the 

 uniting gametes differ in size, as they 

 do in the higher kinds, the smaller one 

 is called the sperm and the larger one 

 the egg. Two sperms, however, can- 

 not form a new organism, nor can two 

 eggs. The union of a sperm and an 

 egg is essential to the production of a 

 new being in this way. With a differ- 



FIG. 81. Cell division 



and the formation of a ence in the size of the gametes, it be- 

 colony 'in green stain (Pleuro- C omes possible to indicate their sex. 



coccus). (Gager.) 



The sperm is always called male, and 



the egg female. In most plants, and in the simpler animals, a 

 single individual may produce both sperms and eggs, but in the 

 higher animals each kind of gamete is produced by a separate 

 individual which is therefore called male or female as the case 

 may be. In plants, the organs of reproduction are found in 

 a complicated structure called the flower. The eggs are pro- 

 duced in one or more bottle-shaped organs called carpels, occu- 

 pying the center of the flower, and the sperms originate in 

 certain cells, called pollen grains, produced by the pin-shaped 

 organs or stamens surrounding the carpels. The transfer of 



