INTRODUCTION. 



All flesh is not the same flesh : but there is one kind of flesh of men, another 

 flesh of beasts, another of fishes, and another of birds. 



SECTION I. 



The Study of Variation. 



To solve the problem of the forms of living things is the aim 

 with which the naturalist of to-day comes to his work. How 

 have living things become what they are, and what are the laws 

 which govern their forms ? These are the questions which the 

 naturalist has set himself to answer. 



It is more than thirty years since the Origin of Species was 

 written, but for many these questions are in no sense answered 

 yet. In owning that it is so, we shall not honour Darwin's 

 memory the less ; for whatever may be the part which shall be 

 finally assigned to Natural Selection, it will always be remem- 

 bered that it was through Darwin's work that men saw for the 

 first time that the problem is one which man may reasonably 

 hope to solve. If Darwin did not solve the problem himself, he 

 first gave us the hope of a solution, perhaps a greater thing. 

 How great a feat this was, we who have heard it all from child- 

 hood can scarcely know. 



In the present work an attempt is made to find a way of 

 attacking parts of the problem afresh, and it will be profitable 

 first to state formally the conditions of the problem and to examine 

 the methods by which the solution has been attempted before. 

 This consideration shall be as brief as it can be made. 



The forms of living things have many characters : to solve the 

 problem completely account must be taken of all. Perhaps no 

 character of form is common to all living things ; on the 

 contrary their forms are almost infinitely diverse. JSJow in those 

 attempts to solve the problem which have been the best, it is this 

 diversity of form which is taken as the chief attribute, and the 

 attempt to solve the general problem is begun by trying to trace 

 the modes by which the diversity has been produced. In the 

 shape in which it has been most studied, the problem is thus the 



b. 1 



