XVI CONTENTS. 



CHAPTER XIII. 



PHYLOGENESIS IN CLASSIFICATION, 



Principles of classification illustrated by the Mollusca and Molluscoidea — 

 The author's philosophy reflected in his classification — Effect of theo- 

 ries of phylogenesis upon classification, 237. — Analytic and synthetic 

 method of classification, 238. — Mollusca and the Brachiopods as illus- 

 trations of evolutional history — Zittel's classification of the branch 

 Mollusca, 239. — Points of view of the embryologist and of the mor- 

 phologist, 240. — Embryological likeness of organisms whose mature 

 characters are diverse — Evolution not traceable between different 

 classes, 241. — General characters of Mollusca — Molluscoidea — Bryozoa 

 — Tunicata — Brachiopoda — The Mollusca (proper) — Lamellibranchs — 

 Gastropoda — Cephalopoda, 242. — Lankester's classification of the Mol- 

 lusca — The Coelomata — Description of the Mollusca — Digestive system 

 — Muscular, nervous, and motory systems — Differentiation of the 

 nervous system — Branches, classes, and subclasses of Mollusca, 246. — 

 Distinctive features of the Lankester classification, 251. 



CHAPTER XIV. 



THE ACQUIREMENT OF CHARACTERS OF GENERIC, FAMILY OR HIGHER 

 RANK; ILLUSTRATED BY A STUDY OF THE BRACHIOPODS. 



Generic and specific evolution illustrated by the Brachiopoda, 253. — Bra- 

 chiopods thoroughly differentiated in early Paleozoic time — Many of 

 them extinct since Paleozoic time, 254. — Generic life-periods of the 

 Brachiopods, 254. — Climax of generic evolution at a definite period, 

 255. — Evolution curves of the Brachiopods — Table of the new gen- 

 era initiated — Its interpretation, 256. — Majority of characters of living 

 Brachiopods traceable to Cambrian ancestors, 258. — Perpetuation and 

 repetition of characters a common law of generation, 259. — Evolution 

 accounts for divergence, not for perpetuation or transmission, 260. — 

 Brachiopods ancient types and early differentiated — Laws of evolution 

 gathered from study of the early families, 261. — Genera making their 

 initial appearance in each era — Comparison of the rate of evolution of 

 generic, family, and ordinal characters — Evolution curves for the 

 several families, 262. — Conclusions from study of generic evolution 

 curves of the Brachiopods, 263. 



CHAPTER XV. 



WHAT IS EVOLVED IN EVOLUTION ?— INTRINSIC AND EXTRINSIC 

 CHARACTERS. 



Laws of evolution indicated by history of Brachiopods — Magellania Jla- 

 vescens examined as an illustration, 265. — Evolution of the class char- 

 acters — Evolution of the ordinal characters, 266. — Calcified loops which 

 are subordinal characters were evolved between the Cambrian and 

 Silurian eras — Each case of evoiution a case of the appearance in 

 some individual of a character not possessed by its ancestors, 267. — 

 Evolution of fundamental characters relatively rapid, 268. — This rapid 



