DARWINISM DEFENDED. 169 



not know the phyletic history of the organ and the 

 function) just how selection could have developed such an 

 organ by slow degrees from slight beginnings. But the 

 secret of the explanation, which is a perfectly consistent 

 Darwinian explanation, lies in the Functionswechsel phe- 

 nomenon. 



"Indifferent characters can suddenly become of selective 

 value through change of environmental conditions or of 

 life-habits. The cranial sutures are certainly of no vital 

 importance with the reptiles and birds, but they can be of 

 very great importance to the viviparous mammals as adapta- 

 tions for passing the pelvis during birth. Lacerta vivipara 

 has, perhaps, no advantage through its viviparousness over 

 its nearly related species in our country, but in Scandinavia 

 it has to thank this peculiarity alone for its success in life,, 

 because the development of its young is rendered inde- 

 pendent of the sun by it. The nectaries were probably at 

 first useless to the flowers ; from that moment, however, 

 when the insects learned to know them as food reservoirs 

 and unwittingly insured cross-pollination by their visits to 

 them, they became of the greatest importance and the indi- 

 rect cause of the origin of the colour brilliance of the 

 flowers. 



There are organs of universal character which can be- 

 come modified in most widely differing directions. Thus 

 the tail of the mammals, originally a long, evenly-haired 

 organ, can, without going through any very elaborate 

 changes, be modified into a bushy steering-rudder of special 

 use in climbing from branch to branch ; or by the outgrowth 

 of a terminal tuft be changed into a flying fan ; or by the par- 

 tial loss of the hair become a grasping organ, or a balancing 

 organ, or an aid in leaping, a rudder in swimming, or a cover 

 against rain and cold (Myrmecophaga jitbata). The append- 

 ages of crabs, the cirri of the annelids, and the teeth of mam- 

 mals are further examples of a similar plasticity and capacity 



