CHAPTER 19 • REPRODUCTION OF LIFE 



1 Does every animal start life as a single cell? 



2 How does the beginning of a new animal resemble the beginning 



of a new plant? 



3 Is there sex in plants, as well as in animals? 



4 How do different kinds of animals reproduce themselves? 



5 Does any animal species reproduce in more than one way? 



6 Do all species of plants produce seeds? 



7 How do seedless plants multiply themselves? 



8 In what ways are eggs and seeds alike? 



9 In what ways are eggs and seeds different? 



The life of every indi\idual, plant as well as animal, comes to an end — 

 after only a few minutes or after many centuries. The rolling seasons bring 

 increase and abundance, followed by drought and killing frost. Whether 

 through privation or illness, through \iolence or mischance, or through the 

 natural internal changes, everyone must die. Dying is part of being alive. 



The life of the individual continues, for longer or for shorter, as the dying 

 protoplasm is constantly replaced within each cell. But while each individual 

 life comes to an end, life goes on. The species or race may continue to live 

 for thousands and thousands of years. How are dying individuals replaced? 

 How does life go on from season to season, from generation to generation? 

 How does a species reproduce itself? 



How Is Reproduction Related to Growth? 



From the End to the Beginning^ Li\ing plant and animal cells often 

 end their existence by dividing into two. When we break a rod of wood or 

 glass into two pieces, we double the number of rods, but we do not increase 

 the amount of wood or glass. Nor do we destroy any glass or wood. We 

 destroy merely the integrity or identity of the original rod. 



In much the same way, a one-celled plant or animal ends its existence by 

 dividing into two. It neither increases nor decreases the amount of proto- 

 plasm. It distributes its living matter between two new cells, which come 

 into being through this process. The mother-cell at the same time destroys 

 its identity; it ceases to exist. We might say that a pleurococcus cell or an 

 ameba is born an orphan. 



Individual cells are constantly being devoured by other organisms, or 

 killed in other ways. W'hen a cell divides, there is a multiplication of cells. 

 We may think of this as a kind of reproduction in one-celled species or as a 



iSee Nos. 1 and 2, pp. 394-395. 

 367 



