IV.
Why all Polygoneutic Species are not Seasonally Dimorphic, p. [63].
Homochronic heredity, [63]. Caterpillars, pupæ and eggs of summer and winter generations of seasonally dimorphic butterflies alike, [64]. The law of cyclical heredity, [65]. Climatic variation of Pararga Ægeria, [68]. Continuous as distinguished from alternating heredity, [68]. Return from dimorphism to monomorphism, [70]. Seasonally dimorphic species hibernate as pupæ, [71]. Retrogressive disturbance of winter generations, [72]. The case of Plebeius Amyntas, [75].
V.
On Alternation of Generations, p. [80].
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].