XIV CONTENTS. 



metazoal organism; generation Agamogenesis, 169. Gamogenesis, 

 170. The several stages of development in the higher organisms, 

 171. The primitive tissues, Endoderm, Ectoderm, and Mesoderm, 

 172. The special organs arising from primitive tissue layers The 

 embryo stage, characterized by dependence and passivity, is not sub- 

 ject to individual struggle for existence, 173. The stage from the 

 free existence of the individual to the maturing of its functions The 

 cell an organism Differentiation of the cell a mark of its organic 

 nature, 174. Differentiation and specialization the marks of an 

 organism, 175. The attainment of heterogeneity Grand results of 

 ontogenesis, or development of the individual, 176. Classification of 

 the functions of a Vertebrate, 177. Are the laws of ontogenesis the 

 same as those of phylogenesis ? The meaning of function, 178. 

 Normal growth Natural Selection, 179. Definition of Ontogeny and 

 Phylogeny The main features of development predetermined before 

 they begin, 180. Slight possible effect of environment, 181. 



CHAPTER X. 



WHAT IS THE ORIGIN OF SPECIES? THE PROBLEM AND ITS 

 EX PL AN A TION. 



Variation and mutability essential presumptions in the discussion of origin 

 of species, 183. Variability an inherent characteristic of all organ- 

 isms The origin of form, not of matter Definition of species whose 

 origin is sought, 184. Meaning of " origin of species " Development 

 of individual characters known and observed The law of develop- 

 ment, 185. No analogy between the origin and development of an 

 immutable species Inorganic properties and organic characters com- 

 pared, 186. The idea of mutability at the foundation of the discussion 

 of the origin of species What is mutable? A concrete example; its 

 characters symbolically represented, 187. Spirifer striatus Martin, 

 var. S. Logani Hall, taken as the example, 188. New species con- 

 ceived of as arising by a process of variable characters becoming 

 permanent, 189. Characters of any particular specimen differ greatly 

 in antiquity, 190. The majority of the characters of a so-called new 

 species have appeared before, 191. Fixed characters those which are 

 transmitted unchanged in natural descent Rank of characters, the 

 precision of their reproduction, and their antiquity, 192. Plasticity of 

 characters Origin of species from the physiological point of view 

 Darwin's theory of the origin of species, 193. Do characters become 

 of higher rank as they are transmitted ? Evolution of genera and ac- 

 celeration and retardation, 196. Growth-force or bathmism The 

 origin of species still an open question, 197. 



CHAPTER XI. 



THE PRINCIPLES OF NA TURAL HISTORY CLASSIFICA TION: ILLUSTRA TED 

 BY A STUDY OF THE CLASSIFICATION OF THE ANIMAL KINGDOM. 



Classifications in Natural History Species and genus of Aristotle, 200. 

 Scaliger's terms The terms of Linne Cuvier's perfection of the 



