CONTENTS. Xlll 



antiquity to distribution, 144. — Table of the Geological range of the 

 families Cerithiidae and Rissoidse — Distribution in relation to the 

 temperature of the waters, 145. — Tabulation of the facts, 146. — Table 

 expressing the relation between the differences in structure of the 

 Gastropoda and different conditions of environment — Summary of 

 results, 147. 



CHAPTER VIII. 



WHAT IS A SPECIES?— VARIOUS DEFINITIONS AND OPINIONS. 



What are species ? Their numbers and importance, 149. — Definitions of spe- 

 cies — Tournefort — Linne — Buffon — De Candolle — Cuvier — Zittel, 150. 

 — The theory of mutability of species and evolution, 151. — Lamarck — 

 Etienne Geoffroy St. Hilaire — Anaximander — Philosophical import- 

 ance of the transmutation theory of the lonians, 152. — Antiquity 

 of the notion of evolution — Reality of species logically antecedent to 

 the notion of specific mutability — The idea of species as immutable, 

 153. — A mutable species necessarily temporary — The question of the 

 mutability of species entirely distinct from that of the origin of 

 species, 154.— The fundamental tenet of the mutability school — 

 State of opinions when Darwin began his investigation of the origin 

 of species, 155. — New conception of the nature of species — Remarkable 

 evolution of thought started by Darwin's "Origin of Species," 156. — 

 Evolution theory of Biology and the uniformitarian theory of Geology — 

 Evolution and Development contrasted, 157. — Evolution the history 

 of the steps by which variation is acquired, not transmitted — A defini- 

 tion of Darwinism, 158. — The Lamarckian theory of evolution — Phylo- 

 genetic evolution, 159. — The fact of evolution established beyond con- 

 troversy; the real nature of evolution to be learned only by a study 

 of the history of organisms — What is an individual? 160. 



CHAPTER IX. 



WHAT IS AN ORGANISM? THE CHARACTERISTICS OF THE INDIVIDUAL 

 AND ITS MODE OF DEVELOPMENT. 



Mutability of organisms a foundation principle of all evolution — Morpho- 

 logical similarity the characteristic of species, 162. — The definition of 

 an organism — Living and performance of physiological functions are 

 essential parts of the definition of an organism — A zoological specimen 

 in the museum as much a vestige of an organism as a fossil, 163. — 

 Living implies change, and change is incessant in a living organism — 

 An organism is an aggregate of cells — The organic cell the morpho- 

 logical unit, 164. — The three ways by which cell modification is accom- 

 plished — Metazoa characterized by Histogenesis, or the formation of 

 tissues, 165. — Histogenesis, Cryptogenesis, and Phylogenesis — Anal- 

 ogy between the cell and organism, and the molecules, elements, and 

 minerals of inorganic matter — The individuality of the organism, 166. 

 — Growth and reproduction of the Protozoa and of the Metazoa con- 

 trasted — Generation the fundamental function of an organism — Sum- 

 mary of the steps of progress in organic development, 167. — Growth — 

 Development — Evolution — Embryology, 16S. — The functions of a 



