x ii FOOT-NOTES TO EVOLUTION. 



PAGE 



chromosome. The ultimate vital units. Significance of 

 reduction. Reduction in Ascaris. Reduction in Crusta- 

 cea. The chromatin as the bearer of hereditary influence. 

 Indirect evidence. Direct experimental evidence. 



VII. THE DISTRIBUTION OF SPECIES . . . . 191 



Illustrations not arguments. Cumulative evidence. 

 The fauna of the Galapagos. Island life. Effects of mi- 

 gration on species. Effects of isolation. Barriers to diffu- 

 sion. Holarctic realm. Neotropical realm. Ethiopian 

 realm. Indian realm. Australian realm. Anomalies in 

 distribution. Adaptation of animals to environment. 

 Invasion of the Australian realm. Trout in Yellowstone 

 Park. Two-Ocean Pass. Laws of distribution of ani- 

 mals. Barriers of land, sea, and climate. Interdepend- 

 ence of species. The arctic birch. Crossing the bar- 

 riers. The flying fish. Subspecies or geographical 

 variations. Doubtful species. Darwin's experience. 

 The shore larks. Work of Dr. J. A. Allen. Species de- 

 fined by missing links. Analogy between variations of 

 species and of words. A fauna like a language. The 

 survival of the existing. How species change with time. 

 Physiological isolation. 



VIII. LATITUDE AND VERTEBRAE 221 



Northern fishes have most vertebrae. Fewest vertebrae 

 in shore fishes of the tropics. Fewer vertebrae indicates 

 greater specialization. Analogy of tropical waters to 

 cities of men. Origin of eels. Coral reefs the centre of 

 fish competition. Cephalization through competition. 



IX. EVOLUTION OF FOSSIL CEPHALOPODA. By Pro- 

 fessor James Perrin Smith ..... 229 



Introduction : General evidence of paleontology ; in- 

 completeness of the record. Law of acceleration of de- 

 velopment. Nomenclature of stages of growth. Paleon- 

 togeny : General statement ; Brachiopoda ; Crustacea ; 

 Mollusca ; Pelecypoda ; Cephalopoda ; Method of work- 



