ORIGIN OF MAN AND THE OTHER VERTEBRATES. 607 



Answering the last question first, it has been conclusively proved 

 that there has been a general correspondence in the progress of verte- 

 brate life in the two continents of the northern hemisphere. The dif- 

 ferences, though numerous, are of minor importance. Some families 

 of vertebrata have existed on the one continent, which were absent 

 from the other, but the number of such is not large. Even the same 

 genus occasionally existed on both continents. 



The other questions must be answered by reference to the gene- 

 alogies themselves, or pbylogenies, as they are called. 



In tracing back all the lines to which we have yet had access, the 

 same kind of changes is found to have taken place in all of them. Let 

 us take, for instance, the animals with hoofs. These embrace the cloven- 

 footed and odd-toed orders, with their many species and families, which 

 are represented by the ox, deer, camel, hog, and hippopotamus, for the 

 cloven-footed ; and the horse, tapir, and rhinoceros, for the odd-toed. 

 Most of these creatures walk on their toes. Many of the first-named 

 group have but two toes, more or less united together, while the horses, 

 of the second group, have but one toe. The bones of the two rows 

 which form both the palm and the sole alternate with each other ; and 

 the ankle-joint is a well-constructed tongue-and-groove arrangement. 

 The teeth in many of them are highly complicated by the infolding of 

 the enamel of the crowns of the molars, and this special development 

 of the molars has been accompanied by a corresponding reduction in 

 their number, and in the number of the incisors. In tracing the lines 

 of these animals backward in time we have made the following discov- 

 eries : First, the infoldings of the enamel of the molars become shal- 

 lower, and are finally represented by the valleys between four hills or 

 tubercles, which stand to each other so as to be inclosed by a square 

 figure. The number of the molar teeth increases. If incisor teeth 

 were absent, they appear. The toes increase in number, becoming five 

 on all the feet. The step becomes plantigrade or flat-footed, the heel 

 reaching the ground. The tongue and groove disappear from the ankle- 

 joint, which becomes flat. The bones of the two rows of the carpus 

 and tarsus no longer alternate with each other, but rest, each one of 

 the first on each one of the second row only. In 1874 I foretold that 

 the ancestor of all the mammals above mentioned would prove to be a 

 " pentadactyle, plantigrade bunodont "; that is, a five-toed sole-walker, 

 with tubercular molar teeth. In 1881, seven years later, I obtained 

 evidence that such a type of mammals abounded in North America 

 during the early Eocene Tertiary period, and the prophecy was ful- 

 filled. The best-known genus of this division has been called Phena- 

 codus, and the figures of it will be found in the " American Natural- 

 ist " for 1884. In a still earlier formation of the Eocene, nearly all the 

 hoofed mammalia were found to be of this type, showing conclusively 

 that this group, which is known as the Condylarthra, was the ancestor 

 of all hoofed mammals (Fig. 1). 



