CONTENTS. XV 



nomenclature and the present usage — ^The classification of Cuvier, 2or. 

 — Uniformity of usage of specific and generic names, 202.— Selection of 

 a standard classification — Differences of opinion regarding the rank of 

 the characters — Claus' and Sedgwick's definitions of the nine branches 

 of the animal kingdom — Protozoa — Coelenterata, 203. — Echinoder- 

 mata — Vermes — Arthropoda — Molluscoidea — Mollusca — Tunicata — - 

 Vertebrata, 204. — The classes of importance in Paleontology and 

 their known range in geological time — Species and genera of chief 

 use in tracing the history of organisms, 205. — The classes of the 

 Animal Kingdom and their geological range, 206. — Species of the 

 paleontologist- — Varieties — Mutations — The history of organisms; the 

 two methods of its study, 207. — Embryos or fossils; the imperfection 

 of the evidence, 208.— Mature individuals, not embryos, used by the 

 Paleontologist — Differentiation attained during the first or Cambrian 

 Era, 2og. — Nature and extent of the elaborations — Recurrence of char- 

 acters accounted for by descent, 211. — Modern zoology applicable to 

 the fauna of the Cambrian Era — Characters whose origin is traced 

 back to Cambrian time — Protozoa, Metazoa — Echinodermata — Anne- 

 lids — Arthropoda, 212. — Insignificance of characters of marine inverte- 

 brates evolved since Cambrian time, 218. 



CHAPTER XII. 



THE TYPES OF CONSTRUCTION IN THE ANIMAL KINGDOM. 



Records of evolution expressed chiefly in generic and specific characters — 

 Course of individual development supposed to have been constant, 

 219. — Beginning of individual life and development — Hypotheses re- 

 garding the phylogenetic evolution of races, 220. — The undifferentiated 

 cell, 221. — Polarity — Antimeres and Metameres — Radiate structure, 

 bilateral symmetry, and actinimeres — Primary axis, 222. — Somites, 

 arthromeres, and diarthromeres of the Arthropods, 224. — Distinc- 

 tive characters of the Metazoa — Molluscan type of structure — De- 

 velopment of organs and their taxonomic rank and value, 225. — The 

 principle of Cephalization, 226. — Cephalization one of the expressions 

 of the general law of differentiation — Meaning of homology and ho- 

 mologous parts — Analogy and analogous parts, 227. — Differentiation 

 illustrated in the case of motor organs — Two directions in which differ- 

 entiation proceeds — Ciliary motion, 228. — Water-vascular system of 

 Echinoderms — Cilia in Molluscoidea and Mollusca — Skeletal parts — 

 Multiplication of like parts preceding specialization of their functions, 

 229. — Comparison between embryonic development and succession of 

 ancestors — Muscular motion or specialized motion, and locomotion, 

 230. — Differentiation of nervous system a concomitant of locomotion, 

 231. — Differentiation along the digestive tract — Differentiation of the 

 motory system into muscular and skeletal organs, 232. — Archetypal 

 structure — Cuvier's classification, 233. — Von Baer's embryological 

 classification — Fundamental divisions of classification discerned by 

 earlier naturalists, 234. — The polymeric type — The dimeric and mono- 

 meric types, 235. — The metameric and diarthromeric types — Meaning 

 of typical structures and types in modern Zoology, 236. 



