486 



BIOLOGY AND HUMAN LIFE 



357. Water essential to gametes. As we have seen, sexual 

 reproduction means the union of two gametes. In addition te 

 producing gametes, bringing them together is another problem 

 of life. Moreover, the sperm and the egg cells (gametes) are 

 unlike spore cells in that they are quite incapable of resisting 



Fig. 204. The four-spined stickleback (Apeltes qiiadraciis) 



The adult fish swims about and through the nest, guarding the eggs while they 



are hatching 



drought ; drying kills them very quickly. A condition essential 

 to reproduction is that the gametes be protected against drying 

 up. Among organisms that live on land or in the air the older 

 methods of bringing the gametes together can no longer serve. 

 We have seen how this condition is met in the flowering plants. 

 Among land animals there are special organs and modes of be- 

 havior that make fertilization possible. 



