CONTENTS 



15 



CHAPTER VI.— Tracheates 



To the tracheates belong spiders and insects. How insects 

 grow. Explanation of the metamorphoses of insects. 

 Protective colouring on the wings of butterflies. The 

 Lamarckian principle refuted by protective colours. 

 Insects that resemble objects. Mimicry. Exhalation 

 from male butterflies. Sexual selection. Origin of 

 flowers due to insects. Parts of the insect's mouth. 

 Refutation of the Lamarckian principle. The coat of 

 insects cannot have arisen by use. Harmonious adapta- 

 tions, co-adaptations. Co-adaptations that Lamarck cannot 

 explain. Explanation of co-adaptations. Are instincts 

 inherited habits? Instincts that can never be affected 

 by the will. Spider's webs. Care of the young. Instincts 

 that are only used once. Are mutilations inherited ? Pro- 

 tective marks, mildew marks, foresight. Infection of 

 embryo. Structure of the embryo. The inheritance of 

 acquired characters is difficult to conceive. Untenability 

 of the Lamarckian principle - 184 



CHAPTER VII.— Crabs and Molluscs 



Economy of nature. The chemical constituents of bodies. 

 Chemical combinations. The elements. The albuminoids. 

 Biogens as constituents of living matter. Vital phenomena 

 and apparent death. Metabolism. Structure of the living 

 substance. Plants the foundation of life. Order of 

 sustenance in nature. Flesh-eating is more natural to 

 the animal than plant-diet. Are all variations useful to 

 animals? Value of selection. Origin of the shells of 

 snails. Change of functions. Development of the crab. 

 Why the embryonic development of an animal reproduces 

 its racial history. Reconstruction of embryogenesis. 

 Uncertainty of the biogenetic law. Parthenogenesis, 

 the development of unfertilised eggs. Significance of 

 the germ -cells. Significance of sexual reproduction. 

 Amphimixis. Plural variations - 228 



CHAPTER VIII.— Worms and Ccelenterata 



Genealogical tree of the animals. Descent of animals. Descent 

 of man. Preservation of intermediate forms. The earth- 

 worm. Regeneration. Leeches. Parasitism. Origin of 



