438 ON THE ORIGIN OF SPECIES 



when we have a definite object in view. We possess no 

 pedigrees or armorial bearings ; and we have to dis- 

 cover and trace the many diverging lines of descent in 

 our natural genealogies, by characters of any kind which 

 have long been inherited. Rudimentary organs will 

 speak infallibly with respect to the nature of long-lost 

 structures. Species and groups of species, which are 

 called aberrant, and which may fancifully be called 

 living fossils, will aid us in forming a picture of the 

 ancient forms of life. Embryology will reveal to us the 

 structure, in some degree obscured, of the prototypes of 

 each great class. 



When we can feel assured that all the individuals of 

 the same species, and all the closely allied species of 

 most genera, have within a not very remote period 

 descended from one parent, and have migrated from some 

 one birthplace ; and when we better know the many 

 means of migration, then, by the light which geology 

 now throws, and will continue to throw, on former 

 changes of climate and of the level of the land, we shall 

 surely be enabled to trace in an admirable manner the 

 former migrations of the inhabitants of the whole world. 

 Even at present, by comparing the differences of the 

 inhabitants of the sea on the opposite sides of a 

 continent, and the nature of the various inhabitants 

 of that continent in relation to their apparent means 

 of immigration, some light can be thrown on ancient 

 geography. 



The noble science of Geology loses glory from the 

 extreme imperfection of the record. The crust of the 

 earth with its embedded remains must not be looked at 

 as a well-filled museum, but as a poor collection made 

 at hazard and at rare intervals. The accumulation of 

 each great fossiliferous formation will be recognised as 

 having depended on an unusual concurrence of circum- 

 stances, and the blank intervals between the successive 

 stages as having been of vast duration. But we shall 

 be able to gauge with some security the duration of 

 these intervals by a comparison of the preceding and 

 succeeding organic forms. We must be cautious in 



