EAMARGEES! THEORY OPE VOLULLION 245 
sidered in another organism which has not, or has 
but slightly, exercised it. It is also very easy to prove 
that the constant lack of exercise of an organ gradu- 
ally reduces it and ends by atrophying it.” 
Then follow the facts regarding the mole, spalax, 
ant-eater, and the lack of teeth in birds, the origin of 
shore birds, swimming birds and perching birds, which 
are stated farther on. 
“Thus the efforts in any direction, maintained for 
along time or made habitually by certain parts of a 
living body, to satisfy the needs called out (erzgés) by 
nature or by circumstances, develop these parts and 
cause them to acquire dimensions and a form which 
they never would have obtained if these efforts had 
not become an habitual action of the animals which 
have exercised them. Observations made on all the 
animals known would furnish examples of this. 
“When the will determines an animal to any kind 
of action, the organs whose function it is to execute 
this action are then immediately provoked by the 
flowing there of subtile fluids, which become the deter- 
mining cause of movements which perform the action 
in question. A multitude of observations support this 
fact, which now no one would doubt. 
“Tt résults from this that multiplied repetitions of 
these acts of organization strengthen, extend, develop, 
and even create the organs which are there needed. It 
is only necessary to closely observe that which is every- 
where happening in this respect to firmly convince 
ourselves of this cause of developments and organic 
changes. 
“However, each change acquired in an organ by 
habitual use sufficient to have formed (oféré) it is 
preserved by generation, if it is common to the in- 
dividuals which unite in the reproduction of their 
