254 Theories Treating of Inheritance 
several nerve centers and unites them by new nerve tracts 
becoming always smoother. These new impressions and 
tracts remain then unaltered in the same places in which 
they were produced and it is just in their continuance 
in the place of their origin that there must be sought the 
reason of the always greater ease with which these 
melodies are reawakened in our memory. When the 
muscles of the hand become accustomed to producing a 
musical exercise, the greater development of the muscles 
and the greater complexity of the nervous co-ordinations 
which connect them with the brain constitute well defined 
material alterations which remain unaltered in the places 
where they arise and make the exercise, at first difficult, 
always easier. 
In the development of the organism on the contrary 
the causes of the repetition each time of always the same 
ontogenetic stages must reside in a single cell, the germ 
cell. But this cell is not in any way the place in which 
are produced the material alterations which were acquired 
by the parent organism and handed over to the descend- 
ants, like the stronger development of certain muscles, 
the greater complexity of certain nervous co-ordinations 
and other similar variations. Of the stronger develop- 
ment of muscles, of the greater complexity of the nervous 
co-ordinations which are produced in the parent organ- 
ism, there remains absolutely nothing, in so far as they 
represent alterations of muscles and nerves, in the little 
particle of matter which is destined to produce the 
descendants. 
Consequently the comparison of the two phenomena, 
although certainly very suggestive, is not sufficient by 
itself to afford in any way an explanation of ontogenetic 
phenomena. 
