46 THE MEANING OF EVOLUTION 
mated with another of her own kind will ever lay an 
egg that will produce a Rhode Island Red. We may 
believe that the dog has descended from some form 
of wolf, but it is not meant that at any particular 
time in the past any wolf mated with a wolf ever pro- 
duced pups that were anything but wolves. 
Why this should be so is one of the most profound 
problems of biology. Nothing but the fact that the 
process has gone on under our eyes for so long a time 
could blind us to its marvelous character. To open 
the egg of a chicken and examine it by the most re- 
fined methods known to science is to find in it abso- 
lutely nothing that could be by the widest stretch of 
the imagination considered anything like a chicken. 
The biologist who has examined such eggs before 
and knows them in all stages of the process may recog- 
nize in an egg which had been incubated for a short 
time something which his previous experience tells 
him will become a chicken. But it has not the faint- 
est resemblance to a chicken until later in its develop- 
ment. In early spring one may gather pond snails 
from any country stream and place them in an aqua- 
rium. The change from the cold water on the out- 
side to the warmer water of the aquarium and the tem- 
perate climate of the room hastens the process which 
in the stream would not take place until later. In a 
short time one may find fastened to the glass side of 
