V Is^ATURAL 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 Avhale tribe among mammals ; 

 to the blind amphibia and insects of the great caverns ; and 

 among plants to the numerous cases in Avhich fioAvers, once 

 specially adapted to be fertilised by insects, have lost their 

 gay corollas and their special adaptations, and have become 

 degi-aded into Avind-fertilised forms. Such are our plantains, 

 our meadow burnet, and even, as some botanists maintain, our 

 rushes, sedges, and grasses. The causes which have led to 

 this degeneration vriW 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 jDreservation 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 occujDy, 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 able to reach, that we find many curious relics 

 of an earlier Avorld, which, in the free air and sunlight and in 

 the great continents, have long since been di^iven out or exter- 

 minated by higher types. 



Summary nf the first Five CJmpfers. 



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 1)y the 

 organic Avorld ; and, also, to discuss some of the theories put 

 forth by modern AVTiters, either as being more fundamental than 



