60 REPRODUCTION 



is too used up to divide; and the egg has too much 

 protoplasm to be stimulated into division by the small 

 amount of nuclear material in it. They do not behave as 

 young cells. They are like two run-down batteries. 



In the second place, these cells are very different in 

 their structure and development. The egg with its large 

 size and rich nutrition is passive and sluggish, while the 

 sperm is reduced to the very lowest living terms. Both 

 these cells are essential to the on-going of the species. 

 Their very differences, therefore, will make it absolutely 

 sure that the powers they have and the work they do 

 must be very different. 



Eggs develop much more slowly, sometimes requiring 

 years; are usually produced in much smaller numbers; 

 have no ability to take an active part in the mating, but 

 secrete substances that attract the male cells. The 

 sperms, on the contrary, are actively sensitive to the 

 substances secreted by the egg or its surrounding tissues, 

 are produced rapidly and in enormous numbers, swim 

 actively about and find the female cells. It is thus seen that 

 their powers and behavior are strongly complemientary 

 and that they are wonderfully adapted to each other: 

 passive and motile, secretion and sensitiveness, attraction 

 and responsiveness, large amount of food substances in 

 protoplasm and almost no protoplasm at all. This 

 adjustment between male and female gametes is the most 

 fundamental fact of sex and mating, and helps determine 

 all the other facts to which we shall give attention later. 



3. Miethod of Fertilization. In the union of the sperm 

 with the egg there are two distinct problems. One is the 

 actual task of uniting these two cells into one when they 

 have come into the same region. The other is that of 

 bringing the sperms and eggs into such close range that 

 they can have any chance of uniting. This latter problem 

 must be solved by the parents that produce the cells, and 

 is solved in very different ways in different plants and 

 animals. It will be considered in the next chapter. 



