KEVIEW OF THE MODERN DOCTRINE OF EVOLUTION. 219 



of origin of these divisions." Since tliat time, Haeckel has pub- 

 lished liis " Gastraa Theory." This is a grand generalization 

 from the facts of embryology, which shows the community in 

 type of the early stages of all animals, and the similarity of the 

 phases which they present during a part of their larval life. The 

 exceptions to this law which have been 

 observed will probably be explained, as 

 have been those which have been urged 

 against the law of homologies in anatomy. 



The paleontology of the Batracliia 

 anura is largely unknown, so we must 

 look elsewhere for proof of the truth of 

 the fourth proposition, viz., that the suc- 

 cessional relation in embryology corre- 

 sponds with that shown by paleontology 

 to have existed in geologic time. 



For this purpose I select one of the 

 most complete series 

 known to paleontology; 

 that of the camels or 

 CameUdcB, whose re- 

 mains are found abund- 

 antly in various parts 

 of our country. The 

 succession of the known 

 genera is seen in the 

 structure of the bones 

 of the feet, and of the 

 superior incisor and 

 premolar teeth. The 

 metatarsal and meta- 

 carpal bones are or are 

 not co-ossified into a 

 cannon bone ; the first 

 and second superior in- 

 cisor teeth are present, 

 rudimental or wanting, 

 and the premolars num- 

 ber from four to one. 

 The relations which 

 these conditions bear 



Fig. 11. 



Fig. 12. 



Fio. 11. — Poehrotheritim vilsoni carpus and meta- 

 carpus with end of radius, three filUis natural size. 

 OriLrinal ; from White Eiver Miocene of Colorado. 



Fm. 12. — Carpus and metacarpus of Procamelus 

 ocridentalis, about two fifths natural size. Oritrinal ; 

 from report of G. M. Wheeler, U. S. Expl. Surv. W. ot 

 100th Mer., vol. iv, pt. ii. From New Mexico. 



