AtfD ABO£T££> ORGANS. 44T 



with modification, we may conclude that tne existence of 

 organs in a rudimentary, imperfect, and useless condition, or 

 quite aborted, far from presenting a strange difficulty, as they 

 assuredly do on the old doctrine of creation, might even have 

 been anticipated in accordance with the views here explained. 



SUMMARY. 



In this chapter I have attempted to show that the arrange- 

 ment of all organic beings throughout all time in groups under 

 groups — that the nature of the relationships by which all 

 living and extinct organisms are united by complex, radiat- 

 ing, and circuituous lines of affinities into a few grand classes 

 — the rules followed and the difficulties encountered by nat- 

 uralists in their classifications — the value set upon charac- 

 ters, if constant and prevalent, whether of high or of the 

 most trifling importance, or, as with rudimentary organs, of 

 no importance — the wide opposition in value between ana- 

 logical or adaptive characters, and characters of true affinity ; 

 and other such rules ; — all naturally follow if we admit the 

 common parentage of allied forms, together with their modi- 

 fication through variation and natural selection, with the 

 contingencies of extinction and divergence of character. In 

 considering this view of classification, it should be borne in 

 mind that the element of descent has been universally used 

 in ranking together the sexes, ages, dimorphic forms, and 

 acknowledged varieties of the same species, however much 

 they may differ from each other in structure. If we extend 

 the use of this element of descent — the one certainly known 

 cause of similarity in organic beings — we shall understand 

 what is meant by the Natural System : it is genealogical in 

 its attempted arrangement, with the grades of acquired 

 difference marked by the terms, varieties, species, genera, 

 families, orders, and classes. 



On this same view of descent with modification, most of 

 the great facts in Morphology become intelligible — whether 

 we look to the same pattern displayed by the different 

 species of the same class in their homologous organs, to 

 whatever purpose applied ; or to the serial and lateral 

 homologies in each individual animal and plant. 



On the principle of successive slight variations, not neces- 

 sarily or generally supervening at a very early period of 

 life, and being inherited at a corresponding period, we can 

 understand the leading facts in embryology; namely, the 



