398 NATURAL SCIENCE [December 
repeats, though very rapidly and indistinctly, the life-history of his 
race, beginning with the unicellular organism and ending, in many 
cases, with the parent. Secondly, that an individual may so vary 
from his parent that he does not recapitulate the whole of the 
phylogeny, and that this constitutes true atavism, true reversion. 
Thirdly, that there is a false atavism, which is really evolution. 
This occurs when an individual after reaching the full development 
of his parent retraces some of the last steps of the ontogeny, and 
so resembles an ancestor more than he does his parent. More need 
not be said concerning the first proposition. As regards the third, 
it has been said above that examples of false atavism are frequent. 
From the nature of the case observation of it is difficult; for in 
every individual this retracement of the ontogeny, this false atavism, 
must be very slight—-so slight as usually to be mappreciable. There- 
fore it is only by observing the retracement, not in an individual 
but in a line of individuals, that it becomes plainly noticeable. It 
is by taking advantage of such retracement that ‘Reversed Selection,’ 
as it has been termed, eliminates a structure which a change of 
environment has rendered not only useless, but worse than useless, 
more rapidly than would otherwise occur under the mere absence of 
selection. For example, Natural Selection has resulted in the evolu- 
tion of eyes. In animals dwelling in absolute darkness, e.g. certain 
cave-dwellers, the eye has become not only useless, but worse than 
useless, since it is an extremely prominent and tender, and therefore 
vulnerable, part of the organism. In some such animals we observe 
that the eye is better developed in the embryo than in the adult. 
Clearly here the animal in its ontogeny retraces some of the steps it 
has already made. Clearly also, if ontogeny be a recapitulation of 
phylogeny, such retracement was made in the phylogeny as well. It 
follows that when a structure, useless both to the embryo and the 
adult, is better represented in the former than in the latter, it must 
have undergone retrogression through the action of reversed selection, 
and that during the phylogeny, after being useful; it became not only 
useless, but worse than useless. 
The second proposition, that an individual may so vary from his 
parent as not to recapitulate the latter stages of the phylogeny, and 
that this constitutes true atavism,is the main proposition of the 
present thesis; but I have yet to prove that this atavism is the cause 
of true retrogression. | 
True atavism can seldom be observed in such of the higher 
animals and plants as have been evolved under Natural Selection, not 
because it does not occur, but simply because it is usually masked 
and slight. It is masked because such complex beings seldom or 
never retrogress in all their characters at once, and, therefore, such 
reversion as may occur in this or that particular is associated with 
