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 Müller, Fritz Müller, 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 connected with pupal conditions.--Origin of wings.--Use of wings under water.--Connection of metamorphoses with alternation of generations.--Parthenogenetic larvæ of _Cecidomyia_.--In alternation of generations one form always agamic.--Dimorphism and Dieidism.--Summary and Conclusions _page_ 62-81