270 Darwin, and after Darwin. 
generations ceased to require their legs, their eyes, 
and so forth, all such organs of high elaboration have 
either disappeared or become vestigial, leaving the 
parasite as a more or less effete representative of its 
ancestry. 
These facts of degeneration, as we have previously 
seen, are of very general occurrence, and it is evident 
that their importance in the field of organic evolution 
as a whole has been very great. Moreover, it ought to 
be particularly observed that, as just indicated, the facts 
may be due either to a passive cessation of selection, or 
to an active reversal of it. Or, more correctly, these 
facts are probably a/aays due to the cessation of 
selection, although in most cases where species in a 
state of nature are concerned, the process of degener- 
ation has been both hastened and intensified by the 
super-added influence of the reversal of selection. In 
the next volume I shall have occasion to recur to 
this distinction, when it will be seen that it is one of 
no small importance to the general theory of descent. 
We may now proceed to consider certain mis- 
conceptions of the Darwinian theory which are largely, 
not to say generally, prevalent among supporters of 
the thcory. These misconceptions, therefore, differ 
from those which fall to be considered in the next 
chapter, i.e. misconceptions which constitute grounds 
of objection to the theory. 
Of all the errors connected with the theory of 
natural selection, perhaps the one most frequently met 
with—especially among supporters of the theory—is 
that of employing the theory to explain all cases of 
