of additional facts bearing on insect fertilisation-Fertilisation of flowers by birds-Self-fertilisation of flowers-Difficulties and con- tradictions-Intercrossing not necessarily advantageous-Supposed evil results of close interbreeding-How the struggle for existence acts among flowers-Flowers the product of insect agency-Concluding The facts to be explained-The conditions which have determined dis- tribution-The permanence of oceans-Oceanic and continental areas -Madagascar and New Zealand-The teachings of the thousand- fathom line-The distribution of marsupials-The distribution of tapirs-Powers of dispersal as illustrated by insular organisms-Birds and insects at sea-Insects at great altitudes-The dispersal of plants -Dispersal of seeds by the wind-Mineral matter carried by the wind -Objections to the theory of wind-dispersal answered-Explanation of north temperate plants in the southern hemisphere-No proof of glaciation in the tropics-Lower temperature not needed to explain What we may expect-The number of known species of extinct animals- Causes of the imperfection of the geological record-Geological evidences of evolution-Shells-Crocodiles-The rhinoceros tribe- The pedigree of the horse tribe-Development of deer's horns-Brain development Local relations of fossil and living animals-Cause of extinction of large animals-Indications of general progress in plants and animals-The progressive development of plants-Possible cause of sudden late appearance of exogens--Geological distribu- tion of insects-Geological succession of vertebrata - Concluding Fundamental difficulties and objections--Mr. Herbert Spencer's factors of organic evolution-Disuse and effects of withdrawal of natural selection-Supposed effects of disuse among wild animals-Difficulty as to co-adaptation of parts by variation and selection-Direct action of the environment-The American school of evolutionists--Origin of the feet of the ungulates-Supposed action of animal intelligence- Semper on the direct influence of the environment-Professor Geddes's theory of variation in plants-Objections to the theory-On the origin of spines-Variation and selection overpower the effects of use and disuse-Supposed action of the environment in imitating varia- tions-Weismann's theory of heredity-The cause of variation-The non-transmission of acquired characters-The theory of instinct-Con- General identity of human and animal structure-Rudiments and varia- tions showing relation of man to other mammals-The embryonic development of man and other mammalia-Diseases common to man and the lower animals-The animals most nearly allied to man- The brains of man and apes-External differences of man and apes— Summary of the animal characteristics of man-The geological antiquity of man-The probable birthplace of man-The origin of the moral and intellectual nature of man-The argument from continuity-The origin of the mathematical faculty-The origin of the musical and artistic faculties-Independent proof that these faculties have not been developed by natural selection-The inter- FIG. PAGE 20. RECOGNITION OF EDICNEMUS VERMICULATUS AND E. SENEGALENSIS (from Seebohm's Charadriada) 223 21. RECOGNITION OF CURSORIUS CHALCOPTERUS AND C. GALLICUS (from Seebohm's Charadriada) 224 22. RECOGNITION OF SCOLOPAX MEGALA AND S. STENURA (from Seebohm's Charadriada) 225 23. METHONA PSIDII AND LEPTALIS ORISE. 241 24. OPTHALMIS LINCEA AND ARTAXA SIMULANS (from the Official Narrative of the Voyage of the Challenger) 247 25. WINGS OF ITUNA ILIONE AND THYRIDIA MEGISTO (from Proceedings of the Entomological Society). 251 26. MYGNIMIA AVICULUS AND COLOBORHOMBUS FASCIATIPENNIS 27. MIMICKING INSECTS FROM THE PHILIPPINES (from Semper's Animal Life). 259 260 28. MALVA SYLVESTRIS AND M. ROTUNDIFOLIA (from Lubbock's British Wild Flowers in Relation to Insects) . 311 29. LYTHRUM SALICARIA, THREE FORMS OF (from Lubbock's British Wild Flowers in Relation to Insects) 312 30. ORCHIS PYRAMIDALIS (from Darwin's Fertilisation of Orchids). 314 31. HUMMING-BIRD FERTILISING MARCGRAVIA NEPENTHOIDES 320 32. DIAGRAM OF MEAN HEIGHT OF LAND AND DEPTH OF OCEANS 345 33. GEOLOGICAL DEVELOPMENT OF THE HORSE TRIBE (from Huxley's American Addresses) 34. DIAGRAM ILLUSTRATING THE GEOLOGICAL DISTRIBUTION OF PLANTS (from Ward's Sketch of Palæobotany). 388 402 35. TRANSFORMATION OF ARTEMIA SALINA TO A. MILHAUSENII (from Semper's Animal Life). 426 36. BRANCHIPUS STAGNALIS AND ARTEMIA SALINA (from Semper's Animal Life). 427 37. CHIMPANZEE (TROGLODYTES NIGER) 454 CHAPTER I WHAT ARE SPECIES," AND WHAT IS MEANT BY Definition of species-Special creation-The early TransmutationistsScientific opinion before Darwin-The problem before Darwin— The change of opinion effected by Darwin-The Darwinian theory -Proposed mode of treatment of the subject. THE title of Mr. Darwin's great work is-On the Origin of Species by means of Natural Selection and the Preservation of Favoured Races in the Struggle for Life. In order to appreciate fully the aim and object of this work, and the change which it has effected not only in natural history but in many other sciences, it is necessary to form a clear conception of the meaning of the term "species," to know what was the general belief regarding them at the time when Mr. Darwin's book first appeared, and to understand what he meant, and what was generally meant, by discovering their origin." It is for want of this preliminary knowledge that the majority of educated persons who are not naturalists are so ready to accept the innumerable objections, criticisms, and difficulties of its opponents as proofs that the Darwinian theory is unsound, while it also renders them unable to appreciate, or even to comprehend, the vast change which that theory has effected in the whole mass of thought and opinion on the great question of evolution. The term " "species" was thus defined by the celebrated botanist De Candolle: "A species is a collection of all the individuals which resemble each other more than they resemble anything else, which can by mutual fecundation |