CHAPTER V 
THE LIFE CYCLE 
46. Birth, growth and development, and death.—Certain 
phenomena are familiar to us as occurring inevitably in the 
life of every animal. Each individual is born in an imma- 
ture or young condition ; it grows (that is, it increases in 
size), and develops (that is, changes more or less in struc- 
ture), and dies. These phenomena occur in the succession 
of birth, growth and development, and death. But before 
any animal appears to us as an independent individual— 
that is, outside the body of the mother and outside of an 
egg (i. e., before birth or hatching, as we are accustomed to 
call such appearance)—it has already undergone a longer 
or shorter period of life. It has been a new living organ- 
ism hours or days or months, perhaps, before its appear- 
ance tous. This period of life has been passed inside an 
egg, or as an egg or in the egg stage, as it is variously 
termed. The life of an animal as a distinct organism be- 
gins in an egg. And the true life cycle of an organism is 
its life from egg through birth, growth and development, 
and maturity to the time it produces new organisms in 
the condition of eggs. The life cycle is from egg to egg. 
Birth and growth, two of the phenomena readily apparent 
to us in the life of every animal, are two phenomena in the 
true life cycle. Death is a third inevitable phenomenon in 
the life of each individual, but it is not a part of the cycle. 
It is something outside. 
47. Life cycle of simplest animals——The simplest animals 
have no true egg stage, nor perhaps have they any true 
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