CHAPTER III 
THE MULTIPLICATION OF ANIMALS AND SEX 
28. All life from life—On the performance of the func 
tion of reproduction or multiplication depends the exist- 
ence or perpetuation of the species. Although an animal 
may take food and perform all the functions necessary to 
its own life, it does not fulfill the demands of successful 
existence unless it reproduces itself. Some individuals of 
every species must produce offspring or the species becomes 
extinct. We have seen in our study of the simple animals 
that the function of reproduction is the first function to 
become differentiated in the ascent from simplest animals 
to complex animals. The first division of labor among the 
cells composing the bodies of the slightly complex animals 
and the first structural differences among the cells are 
connected with the performance of the function of repro- 
duction or multiplication. 
We are all so familiar with the fact that a kitten 
comes into the world only through being born, as the off- 
spring of parents of its kind, that we shall likely not appre- 
ciate at first the full significance of the statement that all 
life comes from life; that all organisms are produced by 
other organisms. Nor shall we at first appreciate the im- 
portance of the statement. This is a generalization of 
modern times. It has always been easy to see that cats 
and horses and chickens and the other animals we famil- 
iarly know give birth to young or new animals of their 
own kind; or, put conversely, that young or new cats and 
horses and chickens come into existence only as the off- 
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