INTRODUCTION 2% 



I much regret that want of space prevents my having 

 the satisfaction of acknowledging the generous assistance 

 which I have received from very many naturalists, some 

 of them personally unknown to me, I cannot, however, 

 let this opportunity pass without expressing my deep 

 obligations to Dr. Hooker, who for the last fifteen years 

 has aided me in every possible way by his large stores of 

 knowledge and his excellent judgment. 



In considering the Origin of Species it is quite con- 

 ceivable that a naturalist, reflecting on the mutual affini- 

 ties of organic beings, on their embryological relations, 

 tlieir geographical distribution, geological succession, and 

 other such facts, might come to the conclusion that 

 species had not been independently created, but had 

 descended, like varieties, from other species. Neverthe- 

 less, such a conclusion, even if well founded, would be 

 unsatisfactory, until it could be shown how the innumer- 

 able species inhabiting this world have been modified, so 

 as to acquire that perfection of structure and coadaptation 

 which justly excites our admiration. Naturalists contin- 

 ually refer to external conditions, such as climate, food, 

 etc., as the only possible cause of variation. In one 

 limited sense, as we shall hereafter see, this may be true; 

 but it is preposterous to attribute to mere external con- 

 ditions the structure, for instance, of the woodpecker, 

 \7ith its feet, tail, beak and tongue so admirably adapted 

 to catch insects under the bark of trees. In the case of 

 the mistletoe, which draws its nourishment from certain 

 trees, which has seeds that must be transported by cer- 

 tain birds, and which has flowers with separate sexes 

 absolutely requiring the agency of certain insects to bring 

 pollen from one flower to the other, it is equally prepos- 



