V 
NATURAL SELECTION 
121 
forms, and also of absolute degradation or degeneration. Ser¬ 
pents, for example, have been developed from some lizard-like 
type which has lost its limbs; and though this loss has enabled 
them to occupy fresh places in nature and to increase and 
flourish to a marvellous extent, yet it must be considered to be 
a retrogression rather than an advance in organisation. The 
same remark will apply to the whale tribe among mammals; 
to the blind amphibia and insects of the great caverns; and 
among plants to the numerous cases in which flowers, once 
specially adapted to be fertilised by insects, have lost their 
gay corollas and their special adaptations, and have become 
degraded into wind-fertilised forms. Such are our plantains, 
our meadow lmrnet, and even, as some botanists maintain, our 
rushes, sedges, and grasses. The causes which have led to 
this degeneration will be discussed in a future chapter; but 
the facts are undisputed, and they show us that although 
variation and the struggle for existence may lead, on the 
whole, to a continued advance of organisation; yet they also 
lead in many cases to a retrogression, when such retrogression 
may aid in the preservation of any form under new conditions. 
They also lead to the persistence, with slight modifications, of 
numerous lowly organised forms which are suited to places 
which higher forms could not fully occupy, or to conditions 
under which they could not exist. Such are the ocean 
depths, the soil of the earth, the mud of rivers, deep caverns, 
subterranean waters, etc.; and it is in such places as these, as 
well as in some oceanic islands which competing higher forms 
have not been aide to reach, that we find many curious relics 
of an earlier world, which, in the free air and sunlight and in 
the great continents, have long since been driven out or exter¬ 
minated by higher types. 
Summary of the first Five Chapters. 
We have now passed in review, in more or less detail, the 
main facts on which the theory of “ the origin of species by 
means of natural selection ” is founded. In future chapters 
we shall have to deal mainly with the application of the theory 
to explain the varied and complex phenomena presented by the 
organic world ; and, also, to discuss some of the theories put 
forth by modern writers, either as being more fundamental than 
