Haeckel’s classification of the phenomena, 80. Proposed modification, 81. Derivation of metagenesis from metamorphosis, 82. Primary and secondary metagenesis, 84. Seasonal dimorphism related to heterogenesis, 86. Heterogenesis and adaptation, 89. Differences between seasonal dimorphism and other cases of heterogenesis, 89. The case of _Leptodora Hyalina_, 93. VI. _General Conclusions_, p. 100. Species produced by direct action of environment, 100. The transforming influences of climate, 103. The origin of variability, 107. The influence of isolation, 109. Cyclically acting causes of change produce cyclically recurring changes, 111. Specific constitution an important factor, 112. A “fixed direction of variation,” 114. _Appendix I._, p. 117. Experiments with _Araschnia Levana_, 117. Experiments with _Pierinæ_, 122. _Appendix II._, p. 126. Experiments with _Papilio Ajax_, 126. Additional experiments with _Pap. Ajax_, 131. Experiments with _Phyciodes Tharos_, 140: with _Grapta Interrogationis_, 149. Remarks on the latter, 152. _Explanation of the Plates_, p. 159. =Part II.= ON THE FINAL CAUSES OF TRANSFORMATION. =I.= THE ORIGIN OF THE MARKINGS OF CATERPILLARS. _Introduction_, p. 161. I. _Ontogeny and Morphology of Sphinx-Markings_, p. 177. The genus _Chærocampa_, 177; _C. Elpenor_, 177; _C. Porcellus_, 184. Results of the development of these species and comparison with other species of the genus, 188. The genus _Deilephila_, 199; _D. Euphorbiæ_, 201; _D. Nicæa_, 207; _D. Dahlii_, 208; _D. Vespertilio_, 209; _D. Galii_, 211; _D. Livornica_, 215; _D. Zygophylli_, 217; _D. Hippophaës_, 218. Summary of facts and conclusions from this genus, 223. The genus _Smerinthus_, 232; _S. Tiliæ_, 233; _S. Populi_, 236; _S. Ocellatus_, 240. Results of the development of these species, 242. The genus _Macroglossa_, 245; _M. Stellatarum_, 245; comparison of this with other species, 253. The genus _Pterogon_, 255; _P. Œnotheræ_, 256; comparison with other species, 256. The genus _Sphinx_, 259; _S. Ligustri_, 259; comparison with other species, 261. The genus _Anceryx_, 264; _A. Pinastri_, 265; comparison with other species, 268. II. _Conclusions from Phylogeny_, p. 270. The Ontogeny of Caterpillars is a much abbreviated but slightly falsified repetition of the Phylogeny, 270. Three laws of development, 274. The backward transference of new characters to younger stages is the result of an innate law of growth, 278. Proof that new characters always originate at the end of the development; the red spots of _S. Tiliæ_, 282. III. _Biological Value of Marking in general_, p. 285. Markings of Caterpillars most favourable to inquiry, 285. Are the Sphinx-markings purely morphological, or have they a biological value? 287. IV. _Biological Value of Colour_, p. 289.