| The Origin of the Different Kinds of Adaptations | [340] |
| – Form and Symmetry | [340] |
| – Mutual Adaptation of Colonial Forms | [350] |
| – Degeneration | [352] |
| – Protective Coloration | [357] |
| – Sexual Dimorphism and Trimorphism | [360] |
| – Length of Life as an Adaptation | [370] |
| – Organs of Extreme Perfection | [371] |
| – Secondary Sexual Organs as Adaptations | [372] |
| – Individual Adjustments as Adaptations | [375] |
| – Color Changes as Individual Adaptations | [375] |
| – Increase of Organs through Use and Decrease through Disuse | [376] |
| – Reactions of the Organism to Poisons, etc. | [377] |
| – Regeneration | [379] |