CONTENTS OF VOL. I. XXlll 



hicrliest functions — The laws of habit are not intelligent — Foi-mation of cellular 



tissue Circulatory vessels, how formed— Cause of circulation in air-breathing 



plants; and in the lowest animals — Tendency of circulation to form channels 

 for itself— Respiratory organs : their variability— Respiration is a physical pro- 

 cess Possible origin of respiratory organs — Homologies of the respiratory 



organs of insects: of air-breathing Vertebrata— Origin of the latter— The 

 axolotl — Stems taking the functions of leaves — Interchange of function between 

 secretory organs — Will purely physical actions account for the origin of all 

 stnictures ? — Organs improve with use : the difficulty is first origin — Origin of 

 nerve and muscle : of the eye and the ear — No physical causes will account for 

 the origin of the eye and the ear; nor of the egg-shell, nor of the skull, nor of 

 nut-shells — Summary Pp. 292 — 307 



CHAPTER XXIV. 



N A T UE A L SELECTION. 



Natural selection defined to be among spontaneous valuations — Causes of variation 

 in domestic races — Changes of circumstances in geological time — Struggle for 

 existence — Races probably mix little in nature — Rapid increase — Favourable 

 variations will be preserved and inherited — Divergence of character, how pro- 

 duced by selection in domestic races, and in wild races — How will incipient 

 races be kept apart ? — By being local — How wild races are kept distinct — Origin 

 of the bat's wing— Extract from Darmn — Flying squirrels — Flying lemur — 

 Bat and flying lemur not descended from a squin-el — Membranes not produced 

 by self-adaptation, but by natural selection — Origin of the bat's wing — Self- 

 adaptation and natural selection co-operating — Extensor muscle of wing of 

 flying lemur — "Will natural selection account for closely correlated or complex 

 organs ? — Quotation from Herbert Spencer — Complexities of the eye and the 

 ear not due to natural selection — Darwin on the simplest eyes — Natm-al selection 

 inapplicable to the highest organization— Improbability equal to impossibility 

 — Algebraic statement — Co-operation of parts in an organ, and of organs in an 

 organism — The eye has been formed on three separate lines of descent — Skulls 

 of Cephalopoda and of Vertebrata — Striated muscular fibre in Annulosa and in 

 Vertebrata — Spontaneous variation and natural selection is a process of blind 

 trial, and inapplicable to complex conditions — Summary — Imitative colouring 

 in birds, in the Polar bear, and in the ermine — The chameleon — Mimicry — 

 Quotation from Darwin — Mr. Bates on mimicry among butterflies — Its purpose 

 is protection — Its cause is natural selection. 

 Note : Formation of Coinplex Organs : — Greyhound — Eyes of amphibious animals. 



Pp. 308—327 



CHAPTER XXV. 



GENERAL KEMAEKS ON THE DEVELOPMENT OF SPECIES. 



Origin of life in Creative Power — Only two theories are possible as to the origin 

 of species : separate creations, or development — Question raised by geological 

 discovery — Difficulties of development theory partly are probably insoluble. 



