122 REPRODUCTION 



that the egg inherits the power and the tendencies from 

 its parents. This only gives a name to the process. Where 

 and how do these powers and tendencies reside in the 

 embryo? 



Development is much more interesting and difficult in 

 the higher animals and plants because it means a great 

 deal more than merely growing. It means becoming 

 different. 



3. What is Development in Higher Forms? There are 

 three important elements in this mysterious process, and 

 while we cannot explain why it takes place by describing 

 these steps, it does make the process seem somewhat 

 clearer to us. 



a. Growth. In the first place growth is important, as 

 it was in the lowly forms. Indeed the larger plants 

 and animals grow more in becoming mature than 

 the simpler ones. Often the increase is a million- 

 fold. The great redwoods of California, which 

 are among our largest plants, and whales, which 

 are about as large animals as have ever lived, arise 

 from eggs that require the microscope to enable us 

 to see them. 



b. Cell Division. When a bacterium divides it makes 

 two bacteria, and thus the individual is kept small. 

 When the egg of a whale divides the daughter cells 

 remain together and we have a two-celled whale 

 embryo. These continue to divide, and since they 

 continue to remain together the embryo comes to 

 have more and more cells. This makes the 

 organism complex. As these cells grow it becomes 

 larger as well as more complex. 



c. Differentiation. Growth and cell division are not 

 easy to explain, but the most difficult thing about 

 development is differentiation. This means that 

 these cells, all derived from one parent cell, are not 

 alike. They may seem to start alike, but great- 

 grand-daughters of the same cell may give rise to 



