Part 20

[247] [Eng. ed. It has frequently been objected to me that the existing Axolotl is not a form resulting from atavism, but a case of “arrested growth.” The expression “atavism” is certainly to be here taken in a somewhat different sense than, for example, in the case of the reversion of the existing Axolotl to the Amblystoma form. Further on, I have myself insisted that in the first case the phyletic stage in which the reversion occurred is still completely preserved in the ontogeny of each individual, whilst the Amblystoma stage has become lost in the ontogeny of the Axolotl. If, therefore, we apply the term “atavism” only to such characters or stages (_i.e._ complexes of characters) as are no longer preserved in the ontogeny, we cannot thus designate the present arrest of the Axolotl at the perennibranchiate stage. Such a restriction of the word, however, appears to me but little desirable, since the process is identical in both cases, _i.e._ it depends upon the same law of heredity, in accordance with which a condition formerly occurring as a phyletic stage suddenly reappears through purely internal processes. It is true that the reversion is not _complete_, _i.e._ the present sexually mature Axolotl does not correspond in all details with its perennibranchiate ancestors. Since Wiedersheim has shown that the existing Axolotl possesses an intermaxillary gland, this can be safely asserted. This gland occurs only in _land_ Amphibians, and therefore originated with the Amblystoma form, afterwards becoming transferred secondarily to the larval stage. Nevertheless, the present Axolotl must resemble its perennibranchiate ancestors in most other characters, and we should be the more entitled to speak of a reversion to the perennibranchiate stage as we speak also of the reversion of single characters. To this must be added that the Axolotl does not correspond exactly with an Amblystoma larva, since Wiedersheim has shown that the space for the intermaxillary gland is present, but that the gland itself is confined to a few tubes which do not by any means fill up this space. (“Das Kopfskelet der Urodelen.” Morph. Jahrbuch, vol. iii. p. 149). By the expression “arrested growth” not much is said, if at the same time the cause of the arrest is left unstated. But what can be the cause why the whole organization remains stationary at the perennibranchiate stage, the sexual organs only undergoing further development? Surely only that law or force of heredity known by its effects, but obscure with respect to its causes, through which old phyletic stages sometimes suddenly reappear, or in other words, that power through which reversion takes place. It must not be forgotten that all these cases of “larval reproduction” in Amphibians appear suddenly. The present sexually mature form of the Axolotl has not arisen by the sexual maturity gradually receding in the ontogeny from generation to generation, but by the occurrence of single individuals which were sexually mature in the perennibranchiate stage, these having the advantage over the _Amblystomæ_ in the struggle for existence under changed climatic conditions.

By admitting a reversion, we perfectly well explain why arrest at the perennibranchiate stage can be associated with complete development of the sexual organs; the assumption of an “arrested growth” leaves this combination of characters completely unexplained. Moreover, I am of opinion that the expressions “arrested growth” or “reversion” are of but little importance so long as the matter itself is clear.]

[248] See Haeckel’s “Anthropogenie,” p. 449.

[249] “Der Ursprung der Wirbelthiere und das Princip des Functionswechsels,” Leipzig, 1875.

[250] Bull. Soc. Neuchâtel. vol. viii. p. 192. Reference given in “Troschel’s Jahresbericht” for 1869.

[251] Sitzungsberichte d. math. phys. Klasse der Akad. d. Wiss. zu München, 1875. Heft i.

[252] Compt. Rend. vol. lxviii. pp. 938 and 939.

[253] Archiv f. Naturgeschichte, 1867.

[254] Compt. Rend. vol. v. 1870, p. 70.

[255] Bull. Soc. Neuchâtel. vol. viii. p. 192. Reference given in “Troschel’s Jahresbericht” for 1869.

[256] [Eng. ed. It was mentioned in the German edition of this work that in the spring of 1876 a female Amblystoma of the Jardin des Plantes in Paris had laid eggs (see Blanchard in the Compt. Rend. 1876, No. 13, p. 716). Whether these eggs were fertile, or whether they developed was not then made known. Thus much was however at the time clear, that even if this had been the case, the reproduction of this Amblystoma would have been only an _exceptional_ occurrence. At that time there were in the Jardin des Plantes Amblystomas which had been kept for more than ten years, and only on one occasion was there a deposition of eggs, and this by only one specimen. That I was correct in speaking of the “sterility” of these Amblystomas in spite of this one exception, is proved by the latest communication from the Jardin des Plantes. We learn from this (Compt. Rend. No. 14, July, 1879, p. 108) that in the years 1877 and 1878 none of the Amblystomas laid any more eggs, although all means were exerted to bring about propagation. In April, 1879, eggs were again laid by one female, and by a second in May. These eggs certainly developed, as did those of 1876, and produced tadpoles. These Amblystomas are therefore not absolutely, but indeed relatively sterile. Whilst the Axolotl propagates regularly and freely every year, this occurs with the Amblystoma but rarely and sparsely. The degree of their sterility can only be approximately established when we know the number of Amblystomas that have since been kept in the Jardin des Plantes. Unfortunately nothing has been said with respect to this.]

[257] Origin of Species, 6th ed. p. 252.

[258] In plants also reversion forms show sterility in different degrees. Mr. Darwin has called my attention to the fact that the peloric (symmetrical) flowers which occasionally appear as atavistic forms in _Corydalis solida_ are partly sterile and partly fertile. That in other causes of sterility, and above all by bastardizing, the reproductive power is lost in the most varying degrees, has been known since the celebrated observations of Kölreuter and Gärtner. [Eng. ed. An Orchid (_Catasetum tridentatum_) has the sexes separate, and the male flowers (_Myanthus barbatus_) differ considerably from the female (_Monachanthus viridis_); besides these, there occurs a form with bisexual flowers which must be considered as a reversion (_Cat. tridentatum_) and _this is always sterile_. Darwin, “Fertilization of Orchids,” 2nd ed. p. 199.]

[259] As we do not know the origin of the “Paris Axolotl” I must restrict myself in the following remarks to _Siredon Mexicanus_ (Shaw).

[260] Mühlenpfordt, “Versuch einer getreuen Schilderung der Republik Mejico,” Hanover, 1844, vol. ii. p. 252.

[261] [The specific gravity of sea water (Atlantic), according to the determinations of Mr. Buchanan on board the “Challenger,” at 15.56° C. varies from 1.0278 to 1.0240. That of the water of the Dead Sea is 1.17205.--Watts’ “Dict. of Chemistry,” vol. v., table, p. 1017. R.M.]

[262] _Loc. cit._ p. 252.

[263] “Über die specifische Verschiedenheit des gefleckten und des schwarzen Erdsalamanders oder Molchs, und der höchst merkwürdigen, ganz eigenthümlichen Fortpflanzungsweise des Letzteren.” Isis, Jahrg. 1833, p. 527.

[264] The experiments referred to have not been made known; I am indebted for them to a written communication kindly furnished by an esteemed colleague.

[265] See Mühlenpfordt’s work already quoted, vol. i.

[266] In the province of botany such a case has already been made known by Fritz Müller (Botan. Zeitung, 1869, p. 226; 1870, p. 149). I may be here permitted to quote a passage from the letter in which Dr. Müller calls attention to this interesting discovery. “As a proof of the possibility that a reversion form can again become a persistent character in a species or in the allied form of a particular district, I may refer you to an _Epidendrum_ of the island of Santa Catharina. In all Orchids (with the exception of _Cypripedium_) only one anther is developed; in very rare cases well-formed anthers appear as reversions among the aborted lateral anthers of the inner whorl. In the _Epidendrum_ mentioned, these are however _always present_.”

[267] [This species is interesting as being ovoviviparous, the young passing through the branchiate stage within the body of the mother. Some experiments, which were partially successful, were made by Fräulein v. Chauvin with a view to solve the question whether the branchiate stage could be prolonged by taking the larvæ directly from the mother before birth and keeping them in water. See “Zeit. für wissen. Zoo.” vol. xxix., p. 324. R.M.]

[268] See Fatiot, “Les Reptiles et les Batraciens de la haute Engadine.” Geneva, 1873.

[269] I can remember at Upper Engadine a peculiar kind of preserved beef, prepared by simply drying in the air; also the mummification of entire human bodies by drying in the open air, as is practised at Great St. Bernard.

[270] “Faune des Vertébrés de la Suisse,” vol. iii. “Histoire Naturelle des Reptiles et des Batraciens.” Geneva, 1873.

[271] See Wiedersheim, “Versuch einer gleichenden Anatomie der Salamandrinen.” Würzburg, 1875.

[272] See Gené, “Memorie della Reale Acad. di Torino,” vol. i.

[273] _Rana esculenta_ never reaches Alpine regions, this species not having been found higher than 1100 meters. (Fatiot, _loc. cit._, p. 318.)

[274] See also the excellent work upon Mexico by Mühlenpfordt already quoted, vol. i., pp. 69-76.

[275] “Essai politique sur le Royaume de la Nouvelle Espagne,” 1805, p. 291.

[276] [The expression made use of by the author, viz. “Diluvialzeit,” would perhaps be more in harmony with the views of English geologists if rendered as the “pluvial period,” thereby indicating the period of excessive rainfall which, according to Mr. Alfred Tylor, succeeded to and was a consequence of the thawing of the great glaciers which accumulated during the last glacial epoch. There is abundant evidence to show that during the latter period glacial action extended in North America at least as far south as Nicaragua. See Belt on “The Glacial Period in North America,” Trans. Nova Scotian Inst. of Nat. Sci. 1866, p. 93, and “The Naturalist in Nicaragua,” pp. 259-265. R.M.]

[277] [Eng. ed. A memoir by Samuel Clarke has since been published upon the embryonic development of _Amblystoma punctatum_, Baird. Baltimore, 1879.]

[278] [Eng. ed. See this author’s work, “Das Kopfskelet der Urodelen.” Leipzig, 1877, p. 149.]

[279] [See preceding note 52. R.M.]

[280] See note 226, p. 566.

[281] [Prof. Semper also remarks (“Animal Life,” note 47, p. 430) with reference to the Axolotl of Lake Como in the Rocky Mountains, which he states always becomes transformed into _Amblystoma Mavortium_, that this metamorphosis “takes place in the water, and the Amblystomas, so long as they are little, actually live exclusively in the water, as I know by my own experience. A young Amblystoma which I kept alive for a long time, never went out of the water of its own free will, while one nearly twice as large lives entirely on land and only takes a bath now and then. It always goes into the water when the temperature of the air in the cellar, in which my aquaria stand, falls below that of the water--down to about 6° or 8° C.” This statement appears to suggest that the effect of temperature may be a factor in some way concerned in these interesting cases of transformation, and would in any case be well worthy of experimental investigation. Some further details concerning the _Siredon Lichenoides_ of Lake Como have been recently published by Mr. W. E. Carlin (Proc. U.S. National Museum, June, 1881). The lake, which is shallow, is fed by a constant stream of fresh water, but the water of the lake is intensely saline. The Siredon never enter the fresh water stream, but congregate in large numbers in the alkaline waters of the lake. “When about one hundred and fifty were placed in fresh water they seemed to suffer no inconvenience, but it had a remarkable effect in hastening their metamorphosis into the Amblystoma form. Of an equal number kept in fresh water and in the lake water, quite a change occurred with the former after twenty-four hours, while the latter showed no change after several days of captivity. Those that were kept well fed in jars usually began to show a slight change in from two to three weeks, and all of them completed the change into the Amblystoma inside of six weeks, while in some kept, but not specially fed, there were but three changes in three months.” (Nature, Aug. 25th, 1881, p. 388.) R.M.]

[282] [Some experiments on the transformation of the Crustacean _Artemia Salina_ into _A. Milhausenii_ by gradually increasing the saltness of the water, and conversely, the transformation of _A. Milhausenii_ into _A. Salina_ by diminishing the saltness of the water, have been made by Schmankewitsch (Zeitschrift f. wiss. Zool. xxv. Suppl. 103 and xxix. 429), but the changes which occur here are much less considerable than in the case of the Axolotl. R.M.]

[283] “Reden und kleinere Aufsätze, Th. II.: Studien aus dem Gebiete der Naturwissenschaften.” St. Petersburg, 1876, p. 81.

[284] This obviously does not imply that the naturalist should not investigate Nature’s processes, and not only correlate these, but also work them up into a universal conception; this is indeed both desirable and necessary if natural knowledge is to be regarded in its true value. The naturalist by this means becomes a philosopher, and the vitality of the so-called “natural philosopher” has been inspired, not by the necessity for investigation, but by philosophy proper.

[285] [The discovery here referred to is the synthesis of urea by Wöhler in 1828 (Pogg. Ann. xii., 253; xv. 619), by the molecular transformation of ammonium cyanate. Since that period large numbers of organic syntheses have been effected by chemists, and many of the compounds formerly supposed to be essential products of life have been built up in the laboratory from their inorganic elements. The division of chemistry into “organic” and “inorganic” is thus purely artificial, and is merely retained as a matter of convenience, the former division of the science being defined as the chemistry of the carbon compounds. R.M.]

[286] “Wahreit und Irrthum im Darwinismus.” Berlin, 1875.

[287] [Eng. ed. I have been reproached by competent authorities for having clothed my ideas upon the theory of selection in the form of a reply to Von Hartmann. I willingly admit that this author cannot be considered as the leader of existing philosophical views upon the theory of descent in Germany; Frederick Albert Lange has certainly a much greater claim to this position. Lange does not however combat this theory; he accepts and develops it most beautifully and lucidly on a sound philosophical basis in such a manner as has never been done before from this point of view (“Geschichte des Materialismus,” 3rd. ed., 1877, vol. ii. pp. 253-277). On most points I can but agree with Lange. Von Hartmann, however, whose objections appeared to me to be supported by a wide scientific knowledge, afforded me a suitable opportunity of developing my own ideas upon some essential points in the theory of selection. In this sense only have I attempted to interfere with this author, the refutation of his views, as such, having been with me a secondary consideration.] [The chief exponent of the doctrine of organic evolution in this country is Mr. Herbert Spencer, in whose “Principles of Biology,” vol. i. chap. xii., will be found a masterly treatment of the theory of descent from a “mechanical” point of view. R.M.]

[288] [The above views on the nature of variability, which were also broadly expressed in the first essay “On the Seasonal Dimorphism of Butterflies” (pp. 114, 115), are fully confirmed by Herbert Spencer (_loc. cit._ chaps. ix. and x.), and more recently by A. R. Wallace in an article on “The Origin of Species and Genera” (_Nineteenth Century_, vol. vii., 1880, p. 93). See also some remarks by Oscar Schmidt in his “Doctrine of Descent and Darwinism,” Internat. Scien. Ser. 3rd. ed. 1876, p. 173. R.M.]

[289] [This law has been beautifully applied by Herbert Spencer in order to explain why, with an unlimited supply of food, an organism does not indefinitely increase in size. “Principles of Biology,” vol. i. p. 121-126. R.M.]

[290] [Eng. ed. This idea, formerly expressed by me, occurs also in Lange (“Geschichte des Materialismus,” ii. 265), and is there exemplified in a very beautiful manner by illustrations from modern chemistry. Lange compares what I have termed above the “physical constitution” of the organism to the chemical constitution of one of those organic acids which by substitution of single elements may become transformed into more complicated acids, but which, as it were, always undergo “further development” in only one determined and narrowly restricted course. Here, as with the organism, the number of possible variations is very great, but is nevertheless limited, since “what can or cannot arise is determined beforehand by certain hypothetical properties of the molecule.”]

[291] “Origin of Species.” 4th German ed., p. 19; 5th English ed., p. 6.

[292] [Mr. A. R. Wallace, in his article last referred to, quotes some most valuable measurements of mammals and birds, showing the amount of variation of the different parts. These observations were published by J. A. Allen, in a memoir “On the Mammals and Winter Birds of East Florida,” &c. (Bulletin of the Museum of Comparative Zoology at Harvard College, Cambridge, Mass., vol. ii. No. 3.) R.M.]

[293] [See note 142, p. 310. R.M.]

[294] “Die Darwin’sche Theorie,” Dorpat, 1875.

[295] [A certain number of instances of mimicry are known to occur between species both of which are apparently nauseous. A most able discussion of this difficult problem is given by Fritz Müller, in the case of the two butterflies _Ituna Ilione_ and _Thyridia Megisto_, in a paper published in _Kosmos_, May, 1879 (p. 100). The author shows by mathematical reasoning that such resemblances between protected species can be accounted for by natural selection if we suppose that young birds and other insect persecutors have to learn by experience which species are distasteful and which can be safely devoured. See also Proc. Ent. Soc. 1879, pp. xx-xxix. R.M.]

[296] See Haeckel’s “Generelle Morphologie,” ii. 107.

[297] “Über die Berechtigung der Darwin’schen Theorie,” Leipzig, 1868.

[298] “Populäre wissenschaftl. Vorträge,” vol. ii., Brunswick, 1871, p. 208.

[299] “Das Unbewusste vom Standpunkte der Physiologie u. Descendenztheorie,” Berlin, 1872, p. 89. The second edition appeared in 1877, in Von Hartmann’s own name.

[300] “Über die Berechtigung,” &c., Leipzig, 1868. In this work will be found briefly laid down the theoretical conception of variability here propounded somewhat more broadly. [In the last edition of the “Origin of Species” Darwin states, with respect to the direct action of the conditions of life as producing variability, that in every case there are two factors, “the nature of the organism and the nature of the conditions.” 6th ed. p. 6. R.M.]

[301] [Although hardly necessary to the evolutionist, it may perhaps be well to remind the general reader, that all experiments upon spontaneous generation, or abiogenesis, have hitherto yielded negative results; no life is produced when the proper precautions are taken for excluding atmospheric germs. But although we have so far failed to reproduce in our laboratories the peculiar combination of conditions necessary to endow colloidal organic matter with the property of “vitality,” the consistent evolutionist is bound to believe, from the analogy of the whole of the processes of nature, that at some period of the earth’s history the necessary physical and chemical conditions obtained, and that some simple form or forms of life arose “spontaneously,” _i.e._ by the operation of natural causes. R.M.]

[302] See Haeckel’s “Generelle Morphologie,” vol. ii. p. 203, and Seidlitz, “Die Darwin’sche Theorie,” 1875, p. 92 _et seq._

[303] [In a recently published work by Dr. Wilhelm Roux this author has attempted to work out the idea of an analogy between the struggle for existence and survival of the fittest in individuals and species, and the struggle for existence and survival of the parts in the individual organism. See “Der Kampf der Theile im Organismus: ein Beitrag zur Vervollständigung der mechanischen Zweckmässigkeitslehre,” Leipzig, 1881. R.M.]

[304] [Eng. ed. Meanwhile it has been shown by Oscar Schmidt that Von Hartmann, under the name of “the Unconscious,” re-invests the old vital force with some portion of its former power. “Die naturwissenschaftlichen Grundlagen der Philosophie des Unbewussten,” Leipzig, 1877, p. 41.]

[305] _Loc. cit._ p. 175.

[306] _Loc. cit._ p. 156.

[307] “Über die Cuninen-Knospenähren im Magen von Geryonien.” Reprint from “Mittheil. des naturwiss. Vereines,” Graz, 1875.

[308] [See Darwin’s “Origin of Species,” 6th ed. pp. 33, 34, and 201-204. R.M.]

[309] [Eng. ed. See Kant’s “Allgemeine Naturgeschichte und Theorie des Himmels.”]

[310] “Das Unbewusste vom Standpunke der Physiologie und Descendenz-Theorie,” Berlin, 1872, p. 16.

[311] [Eng. ed. See Lotze’s “Mikrokosmos,” 1st ed., vol. iii. pp. 477-483.]

[312] See Helmholtz’s “Populäre wissenschaftl. Vorträge,” vol. ii., Brunswick, 1872.

[313] See also Fr. Vischer’s “Studien über den Traum. Beilage zur Augsburger Allgem. Zeitung,” April 14th, 1876. Haeckel also includes this idea in his recent essay already quoted, “Die Perigenesis der Plastidule,” Berlin, 1876, p. 38 _et seq._

[314] See Von Hartmann, _loc. cit._ p. 158.

INDEX.

A.

Abbot and Smith, descriptions of larvæ, 192, 216, 261, 263, 268, 452, 453.

_Acherontia Atropos_, South African form of larva, 263, 324, 531; larva in Spain, 324; larva phytophagically variable, 531.

_Acosmeryx anceus_, larva, 192.

_Acræa_ and Maracujà butterflies as larvæ, pupæ, and imagines, 536.

_Acronycta_, affinities of genus, 169.

Adaptation, 281, 589; analogous, 376; physiological, 590; mutual, 647.

Allen, J. A., variation in birds and mammals, 658.

Alpine form of _P. Napi_, 40.

Alpine hare, seasonal change of colour, 7, 660.

Alternation of generations, 80, 699, 702.

_Amblystoma._ _A. mavortium_ from _Siredon lichenoides_, 567; _A. tigrinum_ bred by Duméril, 567; distribution of species of genus, 569; habits of species, 573; a reversion form, 531, 592; sterility of, 593; oviposition by, 594, 623; definition of genus, 610; degeneration of, 612; causes of reversion of, 600, 608, 613, 620, 631; _A. punctatum_ and _A. fasciatum_, development of, 623; summer sleep of, 628; _A. mavortium_, metamorphosis of, 629.

_Ambulyx gannascus_ and _A. liturata_, larvæ, 245.

Amixia, the principle of, 46, 110.

Ammonites, 275.

_Ampelophaga rubiginosa_, larva, 192.

Amphibia of Upper Engadine, 615.

_Amphiuma_, characters of genus, 579.

_Anceryx_, larva, 264; stages 3, 4, and 5, 266.

_Aphaniptera_, characters of, 498.

Aphides, organic reproduction of, 97.