236 THE MEANING OF EVOLUTION 
and without accounting for them, he built his own 
theory of evolution. He realized his weakness, and 
acknowledged it in his book. He probably did not 
anticipate how insistently later biologists would de- 
mand an explanation that would account for this 
variation. In his later work, responding to this criti- 
cism, Darwin originated a theory which he called 
Pangenesis. He believed that when an adult animal 
had responded to his environment and acquired a new 
character he could transmit this character to his off- 
spring. At that time no one doubted this fact. The 
whole theory of Lamarck was based on the assump- 
tion that this could be done. Darwin suggested that 
every organ of the body threw off minute particles, 
which he called pangenes. These little bodies, car- 
ried by the blood, were taken up by the egg cells or 
sperm cells, and the latter cells determined the future 
development. Consequently, the character of the new 
individual was determined by the parental pangenes. 
In this way the gain acquired by one generation could 
be passed on to the next. This theory was purely 
speculative. He never pretended that there was the 
faintest corroborating evidence visible to the micro- 
scope in the organ, in the blood, or in the germ cell. 
It was not an accounting for what is, but for what it 
seemed possible to him might be. 
This theory of Pangenesis, in the shape in which 
