xii CONTENTS. 



Chrysopa. Libellulidas. Donacia. Spiders. Myriapods. Apod 

 stage of Homomorphous Insects once probably longer than now. 

 Suppression of embryonic stages. Metamorphoses of Hydroida, 

 Crustacea, Isopods, and Amphipocls. Echinoderms. Variations 

 in development induced by the influence of external conditions. 



page 41 62 



CHAPTER IV. 



THE ORIGIN OF METAMORPHOSES. 



Origin of Metamorphoses. Views of Messrs. Kirby and Spence. 

 Nature of the question. Young animals often more similar than 

 mature. Views of Darwin, Herbert Spencer, Johannes Miiller, 

 Fritz Miiller, and Agassiz. Effect of size of egg. Insects leave the 

 egg in a more or less developed condition. Consideration of pupal 

 condition. Quiescence of pupa. Period of quiescence at each 

 moult. Changes not so abrupt as generally supposed. Change in 

 mouth-parts. Difficulty in reference to Darwinian theory. Mouth- 

 parts of Campodea and Collembola, as intermediate between the 

 mandibulate and haustellate types. Change in mouth-parts as con- 

 nected with pupal conditions. Origin of wings. Use of wings 

 under water. Connection of metamorphoses with alternation of 

 generations. Parthenogenetic larvae of Cecidomyia. In alternation 

 of generations one form always agamic. Dimorphism andDieidism. 

 Summary and Conclusions page 62 Si 



CHAPTER V. 



THE ORIGIN OF INSECTS. 



The Origin of Insects. Mistaken views of Darwinian theory. Natural 

 selection a vera causa. Application of Darwin's views to Insects. 

 Similarity of young Crustacea as compared with mature forms ; 

 ditto in Insects. Type of Insecta. Two principal types of larvae : 

 Hexapod and Apod. Conclusions to be drawn from them. Cam- 

 podea the modern representative of the Insect-stock. Campodea, 

 perhaps derived from Tardigrade. Vermiform or Apod type of 

 larva. Views of Fritz Miiller, Brauer, and Packard. Represents 

 a still earlier ancestor. Modern representatives. Notommata, 

 Albertia, Lindia. Earlier forms difficult to trace. Lowest forms 

 of animal life. Yolk-segmentation. Embryology and Evolution. 

 Light thrown by the evolution of the individual on that of the 

 species page 82 108 



