THE STRUGGLE FOR LIFE, 207 
the Vertebrata and the Invertebrata, or those with, and 
those without backbones. The Invertebrata were in exist- 
ence long before the others, which trace their descent 
through them, from their primordial single-celled progenitors. 
Time prevents my treating of the internal life-history of 
any Invertebrata, and even of the Vertebrata I must confine 
myself to their highest and most complex member. 
Whatever the size, complexity, or mental endowments of 
any individual animal may be, in every case, it owes its 
origin to a simple cell. So far as we know, and in this 
case, probably the whole truth is known, there is no such 
thing as spontaneous generation, and the saying ‘‘Omne 
’ or that every living thing comes from an 
egg, is absolutely true. The originally simple cell has how- 
ever to go through much growth and development before it 
vivum ex Ovo,’ 
leaves the body of its mother, as may be shown by an 
examination of the egg of the domestic fowl, when in a fit 
condition to be placed on the breakfast table. 
In all cases the first change is the division of the nucleus 
into two, and this process is continually repeated until the 
yelk is formed: this when complete, consists of a mass of 
very small cells. These during the process of incubation 
become arranged into layers from which the various organs 
of the body are developed. What a wonderful process! 
The originally single and simple cell breaks up into parts 
which acquire the potentiality of forming such diverse organs 
as bone, muscle, and brain. 
However diverse the organs of the body may appear to 
be, when laid bare by the scalpel of the anatomist, they 
are all built up of cells, although they may no longer be 
recognisable as such, owing to their alteration during 
growth; and further, they are all descended from the one 
primordial germ or egg-cell. The hard framework on which 
the body is built up, or bones, the muscles which move 
the bones, the nerves which call the muscles into play, the 
