the pure self-building. Too much income, without 

 activity, begets softness and stagnant life. Yet in youth 

 the building up must be more rapid than the tearing down. 

 This makes growth. 



There is still another way in which this excess which is 

 stored up in youth may be used. Most plants and animals 

 as they approach maturity cease to use the whole of their 

 income for their further growth. Instead, they give ofif 

 portions of themselves, which finally become entirely 

 separate and form other individuals of the same kind. 

 This is called reproduction. It is a kind of growth; but it 

 is growth beyond the limits of the individual. It starts a 

 new individual at the expense of the old. Some of the food 

 which might have gone into the parent goes to build up 

 the new individual. We have found two ways then 

 whereby the individual gets rid of some of its income. 

 These therefore must check its over-growth. They are 

 activity and reproduction. 



4. What Makes an Organism Reproduce? An organism 

 has through its whole life been selfishly laying up in its 

 body the greatest possible amount of material. What 

 could possibly cause it to change its behavior to the very 

 unselfish act of giving a portion of its income, and often a 

 very considerable part of its own body even, to a new 

 individual, whose future will be wholly distinct from it? 

 We have not found a full answer to this question; and yet 

 there are some interesting clues that help us to see how it 

 might have been caused. 



In the simplest kind of organism, a single globular 

 cell, all of the nourishment must be absorbed through the 

 outer wall or surface of the sphere. On the other hand, 

 the amount of nourishment necessary for it is determined 

 by the volume of the same sphere, for the whole volume 

 must be fed. Now as this sphere is nourished and grows, 

 both the surface and the volume increase, but not at the 

 same rate. The surface increases as the square of the 

 radius; but the volume increases as the cube of the radius. 

 For example, if by growing the radius were trebled, the 

 food-taking surface would increase only nine times; 

 whereas the mass that is to be fed would be increased 

 twenty-seven times. This shows that the living thing 

 must keep up a right adjustment between the internal 

 need and the external supply. 



It is important that the student should not fall into an 

 error here. When we ask why an organism does thus 

 and so, we may think of either of two things. We are 

 likely to think of the gain or advantage that will come as 

 the result of doing it and assign this as a reason. Now 

 an advantage lies ahead, always; and events to come can't 

 act as causes, unless the organism is intelligent and can 

 be thought of as looking ahead. We can see in the case 

 above that division would be advantageous. It would 

 increase the surface without changing the volume, and 

 allow more nutrition and more growth. When we ask 

 why, we really mean the cause of the thing. The 

 advantage cannot be the cause. The cause must come 

 before the event. 



Come back to our example. Not all organisms are as 

 simple as the illustration. Yet it is true of all organisms 

 that the food must be absorbed through surfaces, and it is 

 a volume that is to be nourished. We may say that 

 organisms must stop growing near the point where 

 absorption and nutrition are balanced. It may be, when 

 this condition of balance begins to be felt by a growing 

 organism, that this very condition stimulates it to 

 reproduce. This stimulus would be a real cause. In this 

 way the growing power which is lost in the parent is 

 renewed in the offspring, which thus takes onward the 

 torch of life. 



5. What is the Meaning of This? Putting together 

 these two processes, assimilation and reproduction, we 

 have an organism first building itself up in a selfish way 

 through taking in of food and througl^ growth; then, 

 because of this very growth, unselfishly giving a portion 

 of itself to start a new individual life. The student must 

 understand that it is not intended, by the use of the words 

 selfish and unselfish that the organisms are conscious of 

 these tendencies or that they- have any moral meaning. 

 They relate merely to the fact that one tendency and 

 process builds up the self; the other builds up another 

 individual and does it at the expense of the self. 

 Assimilation tends to make the individual continue; but 

 the individual does not live always by this selfish act. 

 We have seen that it always dies. Reproduction is at the 

 expense of this individual, and frequently results in the 

 immediate destruction of the individual; but it starts a 

 new life and thus perpetuates the species. It is interesting 

 that the selfish act has a transient result, while the 

 unselfish act means permanence and continuance of life. 



One of the great truths of life then is this: The best 

 method thus far found in nature to perpetuate life is an 

 alternation of self-building and self-sacrifice, of assimila- 

 tion and reproduction, of emphasis on the individual and 

 emphasis on the species. This alternation is found in 

 practically all organisms. It must be a good thing! 



6. What IS Reproduction? The methods whereby 

 animals and plants reproduce are as widely different as 

 are any other of the facts of life. The remainder of this 

 little book is given to describing some of these methods. 

 We want here to find what, if any thing, is found in all 

 the different kinds of reproduction in the plant and 

 animal kingdoms. We want, in a way, to reduce it to its 

 very lowest terms. Sometimes it is exceedingly simple. 

 Again, it is so covered up and complex that one can 

 scarcely determine the steps. However, reproduction, 

 whether simple or complex, is always this: the division 

 of an organism into two or more. This is the fundamental 

 thing. This is always present in reproduction. This is 

 reproduction. The other facts that we shall find 

 associated with this one are not reproduction. Division 

 of one organism into two or more is the self-sacrificing 

 act that insures that living things shall not disappear 

 from the earth. 



7. Reproduction and the Life-Cycle. The reader will see 

 at once that it is reproduction which makes the cycle. 

 Birth, growth, maturity, decline, and death do not join ends 

 into a cycle. Reproduction is the connection of the passing 

 individual with a new youth. It is the return part of the 

 curve that restores the species to its starting point in spite 

 of the old age and death that overtake the parent. 



CHAPTER THREE. 



CHILDREN OF THE SIMPLEST ORGANISMS. 



1. The Simplest Living Things; 

 Powers. In order to understand the 

 forms of life the student must know 

 the biologist calls a cell. The cell 

 living stuff called protoplasm. It 

 around it. Our bodies and those o 

 and animals are made up of millions 



Their Structures and 



nature of these lowest 

 something about what 

 is a small unit of the 

 commonly has a wall 

 f all the higher plants 

 of cells. Each unit of 



