CONTENTS.

Part I.

ON THE SEASONAL DIMORPHISM OF BUTTERFLIES.

The Origin and Significance of Seasonal Dimorphism, p. [1].

Historical preliminaries, [1]. Does not occur in other orders of insects, [4]. Beginning of experimental investigation, [5]. Lepidopterous foes, [7]. First experiments with Araschnia Levana, [10]. Experiments with Pieris Napi, [13]. Discussion of results, [17]. Origination of Prorsa from Levana, [19]. Theoretical considerations, [23]. The case of Papilio Ajax, [30]. Experiments with Pieris Napi var. Bryoniæ, [39]. The summer generations of seasonally dimorphic butterflies the more variable, [42].

II.

Seasonal Dimorphism and Climatic Variation, p. [45].

Distinction between climatic and local varieties, [45]. The case of Euchloe Belia and its varieties, [47]. The case of Polyommatus Phlæas, [49]. The case of Plebeius Agestis, [50].

III.

Nature of the Causes producing Climatic Varieties, p. [52].

Seasonal dimorphism of the same nature as climatic variation, [52]. How does climatic change influence the markings of a butterfly? [52]. The cause of this to be found in temperature, [54]. Part played by the organism itself, [58]. Analogous seasonal dimorphism in Pierinæ, [60]. The part played by sexual selection, [62].

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].

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].

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.

THE ORIGIN OF THE MARKINGS OF CATERPILLARS.

Introduction, p. [161].

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].

General prevalence of protective colouring among caterpillars, [289]. Polymorphic adaptive colouring in C. Elpenor, C. Porcellus, P. Œnotheræ, D. Vespertilio, D. Galii, D. Livornica, D. Hippophaës, [295]. Habit of concealment primary; its causes, [298]. Polymorphism does not here depend upon contemporaneous but upon successive double adaptation; displacement of the old by a new adaptation; proof in the cases of D. Hippophaës, D. Galii, D. Vespertilio, M. Stellatarum, C. Elpenor, and S. Convolvuli, [300].

Biological Value of special Markings, p. [308].

Four chief forms of marking among Sphingidæ, [309]. Complete absence of marking among small caterpillars and among those living in obscurity, [310]. Longitudinal stripes among grass caterpillars, [312]. Oblique striping. Coloured edges are the shadows of leaf ribs, [317]. Eye-spots and ring-spots. Definition, [326]: Eye-spots not originally signs of distastefulness, [328]; they are means of alarm, [329]; experiments with birds, [330]; possibility of a later change of function in eye-spots, [334]. Ring-spots. Are they signs of distastefulness? Are there caterpillars which are edible and which possess bright colours? [335]; experiments with lizards, [336]. In D. Galii, D. Euphorbiæ, D. Dahlii and D. Mauritanica the ring-spots are probably signs of distastefulness, [341]. In D. Nicæa they are perhaps also means of exciting terror, [342]. The primary ring-spot in D. Hippophaës is a means of protection, [344]. Subordinate markings. Reticulation, [347]. The dorsal spots of C. Elpenor and C. Porcellus, [348]. The lateral dots of S. Convolvuli, [348]. Origination of subordinate markings by the blending of inherited but useless markings with new ones, [349].

VI.

Objections to a Phyletic Vital Force, p. [352].

Independent origination of ring-spots in species of the genus Deilephila, [352]. Possible genealogy of this genus, [358]. Independent origination of red spots in several species of Smerinthus, [360]. Functional change in the elements of marking, [365]. Colour change in the course of the ontogeny, [367].

VII.

Phyletic Development of the Markings of the Sphingidæ. Summary and Conclusion, p. [370].

The oldest Sphingidæ were devoid of marking, [370]. Longitudinal stripes the oldest form of marking, [371]. Oblique striping, [373]. Spot markings, [375]. The first and second elements of marking are mutually exclusive, but not the first and third, or the second and third, [377]. Results with reference to the origin of markings; picture of their origin and gradual complication, [380]. General results; rejection of a phyletic vital force, [389].

II.

ON PHYLETIC PARALLELISM IN METAMORPHIC SPECIES.

Introduction, p. [390].

Larva and Imago vary in Structure independently of each other, p. [401].

Dimorphism of one stage only, [402]. Independent variability of the stages (heterochronic variability), [403]. Constancy and variability are not inherent properties of certain forms of marking, [407]. Heterochronic variability is not explained by assuming a phyletic vital force, [410]. Rarity of greater variability in pupæ. Greater variability more common among caterpillars than among the imagines. Causes of this phenomenon, [412]. Apparent independent variability of the single larval stages. Waves of variability, [416]. Saturnia Carpini an instance of secondary variability, [419]. Causes of the exact correlation between the larval stages and its absence between the larva and imago, [429].

II.

Does the Form-relationship of the Larva coincide with that of the Imago? p. [432].

Family groups, [432]. Families frequently completely congruent, [435]. Exception offered by the Nymphalidæ, [435]. In transitional families the larvæ also show intermediate forms, [441]. Genera; almost completely congruent; the Nymphalideous genera can be based on the structure of the larvæ, [444]. So also can certain sub-genera, as Vanessa, [445]. Incongruence in Pterogon, [450]. Species; incongruence very common; S. Ocellatus and Populi, [451]. Species of Deilephila show a nearer form-relationship as imagines than as larvæ, [454]. Systemy not only the expression of morphological relationship, [455]. Varieties; incongruence the rule; seasonal dimorphism; climatic varieties; dimorphism of caterpillars; local varieties of caterpillars, [456]. Result of the investigation, [458]. Causes of incongruence, [460]. A phyletic vital force does not explain the phenomena, [461]. This force is superfluous, [464].

III.

Incongruences in other Orders of Insects, p. [481].

Hymenoptera. The imagines only possess ordinal characters, [481]. Double incongruence: different distance and different group-formation, [483]. Diptera, [488]. The larvæ form two types depending on different modes of life, [489]. The similarity of the grub-like larvæ of Diptera and Hymenoptera depends upon convergence, [494]. These data again furnish strong arguments against a phyletic vital force, [496]. The tribe Aphaniptera, [498]. Results furnished by the form-relationship of Diptera and Hymenoptera, [499]. Difference between typical and non-typical parts transient, [501].

IV.

Summary and Conclusion, p. [502].

First form of incongruence, [503]. Second form of incongruence, [506]. General conclusion as to the elimination of a phyletic vital force, [511]. Parallelism with the transformation of systems of organs, [513].

Appendix I., p. [520].

Additional notes on the Ontogeny, Phylogeny, &c., of Caterpillars. Ontogeny of Noctua larvæ, [520]. Additional descriptions of Sphinx-larvæ, [521]. Retention of the subdorsal line by ocellated larvæ, [529]. Phytophagic variability, [531]. Sexual variation in larvæ, [534].

Appendix II., p. [536].

Acræa and the Maracujà butterflies as larvæ, pupæ, and imagines, [536].

Explanation of the Plates, p. [546].

Part III.

ON THE FINAL CAUSES OF TRANSFORMATION
(continued).

III.

THE TRANSFORMATION OF THE MEXICAN AXOLOTL INTO AMBLYSTOMA.

Introduction, p. [555].

Experiments, [558]. Significance of the facts, [563]. The Axolotl rarely or never undergoes metamorphosis in its native country, [565]. North American Amblystomas, [570]. Does the exceptional transformation depend upon a phyletic advancement of the species? [571]. Theoretical bearing of the case, [574]. Differences between Axolotl and Amblystoma, [575]. These are not correlative results of the suppression of the gills, [578]. Explanation by reversion, [581]. Cases of degeneration to a lower phyletic stage: Filippi’s sexually mature “Triton larvæ,” [583]. Analogous observations on Triton by Jullien and Schreibers, [591]. The sterility of the artificially produced Amblystomas tells against the former importance of the transformation, [594]. It is not opposed to the hypothesis of reversion, [596]. Attempted explanation of the sterility from this point of view, [597]. Causes which may have induced reversion in the hypothetical Mexican Amblystomas, [600]. Saltness of the water combined with the drying up of the shores by winds, [604]. Consequences of the reversion hypothesis, [609]; Systematic, [609]; an addendum to the “fundamental biogenetic law,” [611]; General importance of reversion, [612]. Postscript; dryness of the air the probable cause of the assumed reversion of the Amblystoma to the Axolotl, [613]. Addendum, [622].

IV.

ON THE MECHANICAL CONCEPTION OF NATURE.

Introduction, p. [634].

Results of the three foregoing essays: denial of a phyletic vital force, [634]. Application of these results to inductive conclusions with reference to the organic world in general, [636]. The assumption of such a force is opposed to the fundamental laws of natural science, [637]. The “vital force” of the older natural philosopher, [640]. Why was the latter abandoned? Commencement of a mechanical theory of life, [642].

Are the Principles of the Selection Theory Mechanical? p. [645].

Refutation of Von Hartmann’s views, [645]. Variability, [646]. The assumption of unlimited variability no postulate of the selection theory, [647]. The acknowledgment of a fixed and directed variability does not necessitate the assumption of a phyletic vital force, [647]. Heredity, [657]. Useful modifications do not occur only singly, [657]. New characters appearing singly may also acquire predominance, [659]. A mechanical theory of heredity is as yet wanting, [665]. Haeckel’s “Perigenesis of the Plastidule,” [667]. Correlation, [670]. The “specific type” depends upon the physiological equilibrium of the parts of the organism, [671]. The theoretical principles of the doctrine of selection are thus mechanical, [675]. Importance of the physical constitution of the organism in determining the quality of variations, [676]. All individual variability depends upon unequal external influences, [677]. Deduction of the limitability of variation, [682]. Deduction of local forms, [686]. Parallelism between the ontogenetic and the phyletic vital force, [687]. The two are inseparable, [690].

II.

Mechanism and Teleology, p. [694].

Von Baer’s exaction from the theory of selection, [694]. Justification of his claim, but the impossibility of the co-operation of a metaphysical principle with the mechanism of Nature, [695]. Per saltum development (heterogeneous generation), [698]. Weakness of the positive basis of this hypothesis, [699]. The latter refuted by the impossibility of the co-operation of “heterogeneous generation” with natural selection, [702]. The interruption by a metaphysical principle cannot be reconciled with gradual transformation, [705]. The metaphysical (teleological) principle can only be conceived of as the ultimate ground of the mechanism of Nature, [709]. Value of this knowledge for the harmonious conception of the Universe, [711]. Explanation of the spiritual by the assumption of conscious matter, [714]. The theory of selection does not necessarily lead to Materialism, [716].

Index p. [719].