parts of the skeleton as in the case of the horse. The metatarsal and 
metacarpal bones are or are not co-ossified into a cannon bone; the 
first and second superior incisor teeth are present, rudimentary or 
wanting, and the premolar number from four to one. The chronological 
succession of genera is given by Mr. Cope as follows: 
No cannon bone. Cannon bone present. 
A 



Tncisor teeth present. Incisors 1 and 2 wanting. 
eS 
4 premolars. 3 premolars, 2 premolars. 1 premolar. 
—_—_—_— 
Lower Miocene . . Poébrotherium. 
Protolabis. 
Upper Miocene . | Procamelus. 
Pliauchenia, 
Camelus. 
Pliocene and recent { ; 
Auchenia. 
According to this table, the Camelide have gradually undergone a 
consolidation of the bones of the feet, with a great reduction in the 
numbers of the incisor or premolar teeth. Mr. Cope indicates an 
interesting parallel between the paleontological succession and the 
embryonic history of the same parts of the skeleton, in the living camel. 
Among the Carnivora, as M. Gaudry has pointed out, it is not only 
possible to trace the ancestry of existing species, but to discover traits 
of union between genera which at present seem far removed.” 
It is not necessary here to enter more fully into the biological 
aspect of this great subject. While the doctrine of evolution has 
now obtained the assent of the great majority of naturalists all over 
the globe, even the most strenuous upholder of the doctrine must 
admit that it is attended with paleontological difficulties which no 
skill or research has yet been able to remove. The problem of 
derivation remains insoluble, nor perhaps may we hope for any 
solution beyond one within the most indefinite limits of correctness.? 

626 PALAONTOLOGICAL GEOLOGY. [Book V. 
. 
But to the paleontologist it is a matter of the utmost importance to 
feel assured that though he may never be able to trace the missing 
links in the chain of being, the chain has been unbroken and 
persistent from the beginning of geological time. as 
It was remarked above (p. 619) that while the general march of | 
life has been broadly alike all over the world yet progress has been 
more rapid in some regions and perhaps in some grades of organic 
being foan in others. It has been suggested that the climatic 
changes which have had so dominant an influence in evolution 
would affect land plants before they influenced marine animals, and 
several instances are adduced where an older type of marine fauna 
is associated with a younger type of terrestrial flora, The flora of 
Fiinfkirchen in Hungary is Triassic in type but occurs in strata which 
have been classed with the Palwozoic Zechstein. The upper 
1 American Naturalist, 1880, p. 172. M. Gaudry traces an analogous process in the 
foot-bones of the ruminants of Tertiary time, “ Les enchainements du Monde Animal,” — 
p. 121. 
2 Op. cit. p. 210. 
3 A, Agassiz, Op. cit. p. 372. 
