Xll CONTENTS. 



inces, 113. — Normal adaptation to conditions of environment — Specific 

 centres of distribution and varieties, 114. — The distinctness of the flora 

 and fauna of distinct provinces — The various classifications of natural- 

 history provinces, 115. — Marine organisms particularly important to 

 the paleontologist — Haeckel's classification of the marine conditions 

 of life — Walther's further analysis of conditions of environment, 116. 

 — Relations of organisms to time and to environment equally signifi- 

 cant, 117. — An explanation required for succession of species as well 

 as for adjustment of species — Evolution and adaptation both observed 

 facts, 118. — Ancestry and environment as causes of evolution — Differ- 

 ences of opinion respecting interpretations, not facts — Introduction of 

 causation into the discussion, 119. — Ancestry and Environment in 

 relation to the beginning of each individual — Definition of the terms 

 "Ancestry" and "Conditions of Environment," 120. — Two factors 

 producing the effects of evolution — Three views possible — First cause 

 of some sort essential to any complete theory of evolution, 121. — 

 Edward Forbes on origin of species and centres of creation — Reality 

 of specific centres not questioned; the fact variously interpreted, 122. 

 — Representative species, common descent, and migration of species — 

 Darwin did not deny the facts, but explained them differently from 

 Forbes — Forbes' explanation of the origin of species, 123. — The mean- 

 ing of evolution by descent — Distinction between Evolution and De- 

 velopment, 124. — Immutability or mutability of species, 125. — Muta- 

 bility of species the central thought in the new theory of the origin of 

 species — Two extremes of opinion regarding the mode of origin of 

 species by evolution, 126. — An unknown cause assumed to explain 

 origins by both Forbes and Lamarck, 127. — Conclusions, 128. 



CHAPTER VII. 



■GEOGRAPHICAL DISTRIBUTION : SPECIAL CONSIDERATION : THE ADJUST- 

 MENT OF ORGANISMS TO ENVIRONMENT. 



Resume, 129. — Gastropoda illustrate the law of relationship between 

 organisms and environment — Meaning of the classification of organ- 

 isms, 130. — Distinguishing characters of the class Gastropoda, 131. — 

 Zones of environment in which Gastropods are distributed, 132. — 

 Reasons for selecting the Gastropods — Peculiarity of the divisions of 

 the Gastropods as to range of adaptation, 133. — Mode of existence of 

 the Glossophora, 135. — The zonal distribution of the Ctenobranchina, 

 136. — Genera of the Ctenobranchina characteristic of the several 

 bathymetric zones, 137. — Evidence of the adjustment of the morpho- 

 logical characters to environment — Law of the adjustment of organ- 

 isms to conditions of environment, 138.— Summary, 139. — Relation 

 between zonal adaptation and geographical range, 140. — Families 

 whose genera have a very wide range of adaptation, and restricted 

 adjustment only among the species — Great difference in the closeness 

 of adjustment of the characters of different taxonomic rank, 142. — 

 Species generally closely adjusted to particular conditions — Fresh- 

 water families; restriction in their distribution — Two closely allied 

 families separated in their distribution, 143. — Table of the Geological 

 range of the families Strombidae and Chenopodidae, 144. — Relation of 



