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 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 larvæ: Hexapod and Apod.—Conclusions to be drawn from them.—_Campodea_ the modern representative of the Insect-stock.—_Campodea_, perhaps derived from Tardigrade.—Vermiform or Apod type of larva.—Views of Fritz Müller, 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 DESCRIPTION OF THE PLATES. PLATE I. p. 7. FIG. 1. Cricket. Westwood, Intro. to the Modern Classification of Insects, vol. i. p. 440. 2. Earwig. Westwood, loc. cit. vol. i. p. 399. 3. _Aphis_. Packard, Guide to the Study of Insects, pp. 521, 522. 4. _Scolytus_. Westwood, loc. cit. vol. i. p. 350. 5. _Anthrax_. Westwood, loc. cit. vol. ii. p. 538. 6. _Balaninus_. 7. _Cynips_. Westwood, loc. cit. vol. ii. p. 121. 8. Ant (_Formica_). Westwood, loc. cit. vol. ii. p. 218. 9. Wasp. Ormerod, Nat. Hist. of Wasps, pl. i. fig. 1. PLATE II. p. 8. FIG. 1. Larva of Cricket. Westwood, loc. cit. vol. i. p. 440. 2. Larva of _Aphis_. Packard, loc. cit. pp. 521, 522. 3. Larva of Earwig. Westwood, loc. cit. vol. i. p. 399. 4. Larva of _Scolytus_. Westwood, loc. cit. vol. i. p. 350. 5. Larva of _Anthrax_. Westwood, loc. cit. vol. ii. p. 546. 6. Larva of _Balaninus_. 7. Larva of _Cynips_. Westwood, loc. cit. vol. ii. p. 121. 8. Larva of Ant (_Formica_). Westwood, loc. cit. vol. ii. p. 226.