CONTEXTS ix 



PACK 



Simplicidentata, \>. 14."). Duplicidentata, ]. 148. Tillodontia, )>. 151. 

 Superorder I'ngnlata, p. H>3. Aml>l\p<>da, p. Mil. Condylarthra, p. K!N. 

 Artiodactyla, p. 171. Perissodaetyla, p. 171. Chalicotheroidea or An- 

 rylopnda, ]>. 1S4. Hyracoidea, }>. IS."). Proboscidea ]>. isfi. Sirenia, 

 p. 18S. South American Ungulates, p. 189. ( 'etacea, p. 19O. Zeug- 

 . 191. 



CHAPTER VIII. 



EVOLUTION OF THE PREMOLAKS, 193 



Premolars in primitive M annuals, p. 193. Adaptation <>f prenmlars, 

 |i. 191. Various upper premolar types, p. 194. Cusp addition in the pre- 

 inolars, p. 19"). Superior premolars, ]). 19"). Inferior premolars, p. 198. 



CHAPTEK IX. 

 OBJECTIONS AND DIFFICULTIES, AND OTHER THEORIES. 



I. That the tritubercular type is not primitive : 



1. The plexodbnt or progressive simplification theory of Ameghino, - 201 



2. Objections by Fleischmann and Malm answered by Scott, 204 



3. The primitive polybuny theory, 205 



II. That the Cope-Osborn theory of the origin of the superior molars 



is incorrect, 208 



1. (Aisp homologies founded on embryogeny, p. 208. Order of em- 

 bryonic cusp-development in Insectivora, p. 210. Summary of 

 Woodward's conclusion, p. 212. Ontogenetic order according to 

 Marett Tims, p. 213. The premolar analogy, theory, p. 215. 

 Palseontological difficulties in the premolar analogy theory, p. 217. 

 Gidley's restudy (1906) of Jurassic Mammals supports embryo- 

 geny and the premolar analogy theory, p. 219. Addendum: the 

 " trituberculy " of Zalambdodonts a secondary acquirement or 

 u pseudo-trituberculy," p. 225. Conclusion, p. 227. 



CHAPTEK X. 

 RECTIGRADATIONS IN THE TEETH, 229 



Homoplasy as a law of latent or potential homology, p. 229. Homologv, 

 p. 237. Lankester's reply to the preceding article, p. 238. 



BIBLIOGRAPHY, 240 



