CONTENTS. Xlll 



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

 families Cerithiidse and Rissoidae 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. 



WHA T 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 ta 

 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 Tl^e 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 aifd 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, 168. The functions of a 



