Part I.

ON THE SEASONAL DIMORPHISM OF BUTTERFLIES.

I.

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.

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.

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.

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.

V.

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.

I.

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.

I.

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.