XX CONTENTS. OF VOL. I. 



tribution of Mammalia in the old continents, Australia, South America, and 

 Madagascar — Wingless birds of New Zealand — Extinct animals of each region 

 resemble the liying ones — Resemblance of species in conformable strata — Con- 

 nexion by descent, but modified — Foreign species gaining on native ones — 

 Upland goose — Ground woodpecker — Bats on remote islands — Birds on the 

 same, unable to fly — The dodo — The solitaire — The dinornis — The apteryx — 

 Origm of such races — Cuvier's principle will not explain the facts of distribu- 

 tion — These facts support the theory of descent with modiiication. 



Pp. 219—227 



CHAPTER XIX. 



MORPHOLOGY. 



Fimctional adaptations — Structural adaptations — Is all morphology explicable by 

 the law of adaptation ? — Statement of that law — Crj'stalline and organic mor- 

 phology — Formative laws of crystallization indei^endent of function — The same 

 probably true, in part, of organic forms — Acauthometrse — Correlations in all 

 organisms not referable to adaptation — Classes of homologies — Homologies of 

 the parts of a tree in flower — Metagenesis of Hydrozoa — Flower-like organs — - 

 Medusae — In what sense metagenesis occurs in flowering plants — Homologies of 

 the parts of Hydrozoa : of flowering plants — Umbelliferee — Their correlations 

 not due to adaptation — Difi'erences of the sexes not fundamental — Secondary 

 sexual characters are variable — Metamorphosis in Insects, Batrachians, and 

 Crustacea — Cirrhipedes — Retrograde metamorphosis — Echinoderms — Resem- 

 blance between the forms of the same species — We might expect this — Nipples 

 in man — Relations of parts of the individual — Homology of hands and feet — 

 Their tendency to vary together, like similar parts of crystals — Only ungulate 

 animals have horns — Reason suggested— Position of horns — Rhinoceros — Re- 

 semblances of difTerent parts in the same organism — Vertebrata — Articulata — 

 MoUusca — Crinoids — Summary of facts — Correlation and adaptation distinct — 

 Ciystalline and organic morphology. 



Note : — Approach to metagenesis in Vallisneria spiralis . . . Pp. 228—240 



. CHAPTER XX. 



COMPAKATIVE MORPHOLOGY. 



Specific morphology logically comes before comparative — Analogy and homology 

 ^Wing of bird and of insect — Lungs and swim-bladder — Homologies of respira- 

 tory organs variable^ Analogies and homologies within the species — Legs and 

 arms of Crastacea — Jaws of Articulata— Fins of fishes — Homological resem- 

 blances carried further than necessary — Homological resemblances and adaptive 

 difi'erences — Hand, foot, wing, and paddle, all homologous — Adaptation wiU 

 not account for homology — Vertebra; separate in the lower Vertebrata, partly 

 united in the higher— How is homology to be explained ? — Unity of plan is no 

 explanation — No law subject to exceptions can be ultimate— Exceptions to 

 plan— Cervical vertebrse of Mammalia— Intelligent and unintelligent powers— 



