106 DEVELOPMENT AND HEREDITY. 



Let US now attempt to apply these general princi- 

 ples, and try to explain the development of a hypo- 

 thetical first organism ; for, since the state of living 

 matter is dependent on all its past history, we must 

 naturally begin at the beginning in order to explain 

 the changes which living matter has undergone. It 

 is possible in this way to illustrate the theory by a 

 typical case, if we carefully keep within the limits of 

 the general principles of evolution, as it may be in- 

 ferred from the visible organic world and the traces 

 of its past history. Let us imagine an organism, 

 consisting of a simple, undifferentiated mass of pro- 

 toplasm, to have come into existence without any 

 inherited powers or tendencies. There are no ner- 

 vous co-ordinations or associations. All of its move- 

 ments and reactions are dependent merely on its 

 chemical and physical conditions and upon the forces 

 which affect it. In the first instant of its existence, 

 this highly sensitive and mobile organisation of mat- 

 ter is subject to the action of a variety of forces. 

 There, are the forces of pressure exerted by the 

 medium in which the organism lives, and by the sup- 

 porting body upon which it rests. There are also 

 the forces exerted by things brought into contact 

 with the organism by movements of the surrounding 

 medium. Some strike or press against the outer 

 surface of the organism. Others are forced into the 



