THE EVOLUTION OF ORGANIC BEHAVIOUR 39 
mind that they not only work for their own generation, but 
they determine the course of heredity. Picture two such 
communities set in an environment which intensifies the 
struggle for existence. The one is strong, healthy, and 
vigorous ; the other in all respects the reverse. The incidence 
of the battle of life falls mainly on the workers. If they 
succumb in the one group their fertile queen either perishes, 
or gives rise to a poor stock, certain in the Jong run to be 
eliminated. But the vigorous workers in the other group 
survive and secure, too, the survival of their queen, who, since 
she is also their sister, bears, in her ovaries, the good seed from 
which a new generation of vigorous workers shall be developed. 
Thus though the sterile bees contribute nothing directly to 
the heredity of the race, they indirectly determine the direction 
which that heredity shall take. So, too, in the higher animals, 
the reproductive cells are the fertile sisters of a host of sterile 
body cells, on which the main incidence of the struggle for 
existence falls. Their sterility precludes their directly con- 
tributing to the success of future cell-generations ; but in 
protecting their fertile sisters, the reproductive cells, they are 
really determining the lines along which the evolution of the 
race shall continue. 
Acquired characters may thus be regarded as the results of 
those accidents, fortunate or the reverse as the case may be, 
which happen to the body, and more or less modify its outward 
form or hidden structure, and its modes of organic behaviour ; 
but which, as such, have no direct effects for better or worse 
on the germinal substance. All that the plant or animal can be 
is due to heredity ; all that it és, to heredity and circumstance. 
Even the ability to yield to circumstance is part of heredity’s 
dower. Fortunate, then, the plant or animal that inherits such 
definiteness of structure and behaviour as may fit it to its 
station, together with such plasticity as may enable it to 
accommodate itself to those changes of environing conditions 
which may fall to its lot. 
One more point must be noticed in connection with 
this difficult and puzzling subject. The acceptance of the 
