﻿part 1] ANKIYEESAltY ADDRESS OF THE PRESIDENT. lxxiii 



the foot was displaced outwards from the third to the fourth toe. 

 In other words, an essentially ungulate foot was produced as usual, 

 only disturbed by an initial twist. 



From these and many similar facts in mammalian evolution, we 

 may therefore conclude that parallel development or ' homoeo- 

 morphy ' undoubtedly occurs. Some of the changes are adaptations 

 to the same altering modes of life, perhaps also to the same 

 progressive modifications in the environment ; among which may 

 be enumerated the increasing efficiency of the teeth for grinding 

 and of the feet for running. Other changes are the inevitable 

 marks of racial maturity or old age, such as increase of size, the 

 development of excrescences, and the reduction in number of the 

 teeth. While, however, both these series of changes always take 

 place in approximately the same order and may be used to mark 

 the successive periods of Tertiary time by a paleontologist who is 

 accustomed to deal with such evidence, there is still no reason to 

 suppose that identical animals have arisen from more than one 

 som'ce. Distinct families or genera which may be difficult to 

 separate on superficial examination, are readily recognized in most 

 cases when studied in detail with our present knowledge of general 

 principles. It is, indeed, usually possible to distinguish between 

 traits of heredity that are fundamental, and those that are merely 

 adaptive or depend on racial antiquity. The new palaeontology 

 is thus as useful in relation to world-problems, as was the old 

 palaeontology in determining the relative ages of the rocks in the 

 restricted European area to Avhich it was first applied. 



The adaptive characters just mentioned change with much 

 rapidity, and allow a tolerably detailed subdivision of the series of 

 strata which contain the fossils exhibiting them. It is therefore 

 interesting to notice that some other characters which can scarcely 

 be correlated with utility or efficiency, persist without change for 

 comparatively long periods and are of little value for stratigraphical 

 geolog} r . Huxley long ago directed attention to the problem of 

 ' persistent types,' as he termed them, and most of them are still 

 as inexplicable as they were when first considered. Only in the 

 case of certain fishes have I suggested that advance was stopped 

 by the appearance of various modifications or specializations in the 

 wrong order. It may be that single peculiar characters persist 

 when they cannot be affected by Natural Selection. One of the 

 most striking examples was described by Egerton in the Society's 

 Journal for 1871 in a Chimaeroid fish from the Lower Lias of 



