INTRODUCTION. 



several statements ; and I must trust to the reader reposing some 

 confidence in my accuracy. No doubt errors will have crept in, 

 though I hope I have always been cautious in trusting to good 

 iuthorities alone. I can here give only the general conclusions at 

 which 1 have arrived, with a few facts in illustration, but which, 

 I hope, in most cases will suffice. No one can feel more sensible 

 i/han I do of the necessity of hereafter publishing in detail all the 

 facts, with references, on which my conclusions have been grounded ; 

 and I hope in a future work to do this. For I am well aware that 

 scarcely a single point is discussed in this volume on which facts 

 cannot be adduced, often apparently leading to conclusions directly 

 opposite to those at which I have arrived. A fair result can be 

 obtained only by fully stating and balancing the facts and argu- 

 ments on both sides of each question ; and this is here impossible. 



I much regret that want of space prevents my having the satis- 

 faction of acknowledging the generous assistance which I have 

 received from very many naturalists, some of them personally un- 

 known 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 conceivable that 

 a naturalist, reflecting on the mutual affinities of organic beings, 

 on their embryological relations, their geographical distribution, 

 geological succession, and other such facts, might come to the con- 

 clusion that species had not been independently created, but had 

 descended, like varieties, from other species. Nevertheless, such a 

 conclusion, even if well founded, would be unsatisfactory, until it 

 could be shown how the innumerable species inhabiting this world 

 have been modified, so as to acquire that perfection of structure 

 and coadaptation which justly excites our admiration. Naturalists 

 continually refer to external conditions, such as climate, food, &c, 

 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 conditions, the structure, for instance, of 

 the woodpecker, with 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 certain 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 preposterous to account for the structure of this parasite, 

 with its relations to several distinct organic beings, by the effects 



