Chapter II: Mechanism and Teleology (1)

In the third volume of his smaller works Karl Ernst von Baer submits the theory of selection to a most searching examination. Without actually calling in question its scientific admissibility, he believes that this theory is dependent upon its satisfying one condition, viz. that it should connect the teleological with the mechanical principle.

“The Darwinian hypothesis, as stated by its supporters, always ends in denying to the processes of nature any relation to a future, _i.e._ any relation of aim or design. Since such relations appear to me _quite evident_,” &c. And further:--“If the scientific correctness of the Darwinian hypothesis is to be admitted, it must accommodate itself to this universal striving after a purpose. If it cannot do this we should have to deny its value.”

These words appear almost equivalent to passing a sentence of doom upon the theory of selection and the mechanical conception of nature, for how can one and the same process be effected simultaneously by necessity and by designing powers? The one excludes the other, and we must--so it appears--take our stand either on one side or the other.

Nevertheless we cannot set aside Von Baer’s proposition without further examination simply because it is apparently incapable of being fulfilled, since it contains a truth which should not be overlooked, even by those who uphold the mechanical theory of nature. It is the same truth which is also made use of by the philosophical opponents of this theory, viz. that the universe as a whole cannot be conceived as having arisen from blind necessity--that the endless harmony revealed in every nook and corner by all the phenomena of organic and of inorganic nature cannot possibly be regarded as the work of chance, but rather as the result of a “vast designed process of development.” It is also quite correct when, in reply to the supposed objection that the mechanical theory of nature is not concerned with chances but with necessities, Von Baer answers that the operations of a series of necessities which “are not connected together” can only be termed accidents in their opposing relations. He illustrates this by instancing a target. If I hit the latter by a well-aimed shot, nobody would explain this as the result of an accident, but if “a horseman is riding along a gravelly road past this target, and one of the pebbles thrown up by the hoof of the galloping horse hits the mark, this would be termed an accident of extremely rare occurrence. My target was not the mark for the pebble, therefore the hit was purely accidental, although the projection of the stone in this precise direction with the velocity which it had acquired, was sufficiently explained by the kick given by the horse. But the hit was accidental because the kick of the galloping horse, although it necessarily projected the pebble, had no relation at all to my target. For the same reason we must regard the universe as an immense accident if the forces which move it are not designedly regulated--the more immense because it is not a single motion of projection that acts here, but a large number of heterogeneous powers, _i.e._ a large number of variously acting necessities which are, as a whole, devoid of purpose, but which nevertheless accomplish this purpose, not only at any single moment, but constantly. A truly admirable series of desirable accidents!”[305]

The same idea is expressed, although in a very different manner, by Von Hartmann, in the concluding chapter of his work already quoted. He thinks that “design is a necessary and certain consequence of the mechanical laws of nature.” “Were the mechanism of natural laws not teleological there would be no mechanically regulated laws, but a weak chaos of obstinate and capricious powers. Not until the causality of the laws of inorganic nature had superseded the expression “dead” nature, and had shown itself as the mainspring of life and of a conformability to design visible on all sides, did it deserve the name of mechanical lawfulness; just as a complication of wheels and machinery made by man, which move in some definite manner with respect to one another, only acquires the name of a mechanism or of a machine when the immanent teleology of the combination and of the various movements of the parts is revealed.”[306]

Against the correctness of the idea underlying these statements scarcely anything can in my opinion be said. The harmony of the universe and of that portion of it which we designate organic nature, cannot be explained by chance, _i.e._ without a common ground for co-operating necessities; by the side of mere mechanism it is impossible not to acknowledge a teleological principle--the only question is, in what manner can we conceive this as acting without abandoning the purely mechanical conception of nature?

This is obviously effected if, with Von Baer and Von Hartmann, we permit the metaphysical principle to interrupt the course of the mechanism of nature, and if we consider both the former and the latter to work together with equal power. Von Hartmann expressly makes such an admission under the name of an “internal principle of development,” to which he attributes such an important share that one cannot understand why it should have any need for the employment of causal powers, and why it does not simply do everything itself. Von Baer expresses himself much less decisively, and even in many places insists upon the purely mechanical connection of organic natural phenomena; but that with him also the idea of interruption by a metaphysical principle is present, is principally shown by his assuming, at least partly, the _per saltum_ development of species. This necessarily involves an actively internal power of development.

Although I have already brought forward many arguments against the existence of such a power, and although in refuting it every form of development by directive powers is at the same time overthrown, it nevertheless appears to me not to be superfluous in such a deeply important question to show that a _per saltum_ development, and especially the so-called heterogeneous generation, is inconceivable, not only on the ground of the arguments formerly employed against the phyletic vital force in general, but quite independently of these.

In the first place it must be said that the positive basis of this hypothesis is insecure. Cases of sudden transformation of the whole organism with subsequent inheritance are as yet quite unknown. It has been shown that the occasional transformation of the Axolotl must most probably be regarded in a different light. Another case, taken for heterogeneous generation, viz. the budding of twelve-rayed Medusæ in the gastric cavity of an eight-rayed species, has lately been shown by Franz Eilhard Schulze[307] to be a kind of parasitism or commensalism. The buds of the _Cuninæ_ do not spring, as was supposed, from the _Geryonia_, but are developed from a _Cunina_ egg. But even if we recall here the cases of alternation of generation and heterogenesis, this would not be of any value by way of proof; it would only be thus indicated how one might picture to oneself a sudden transformation. That in alternation of generation, or generally, in every mode of cyclical reproduction, we have not to deal with the abandonment of one type of organization and the transition to some other, is proved by the continual return to the type of departure--by the cyclical character of the entire transformation. That two quite heterogeneous types can belong to one cycle of development is, however, capable of a far better and more correct explanation than would be given by the supporters of _per saltum_ development. If we trace cyclical reproduction to the adaptation of different developmental stages or generations to deviating conditions of life, we thus not only explain the exact and often striking agreement between form and mode of life--we not only bridge over the gap between metamorphosis and alternation of generation, but we can also understand how, within one and the same family of Hydrozoa, species can occur with or without alternation of generation, and further how other species can exist in which the alternation of generation (the production of free Medusæ) is limited to the one sex; we can understand in general how one continuous series of forms may lead from the simple sexual organ of the Polypes to the independent and free swimming sexual form of the Medusæ, and how hand in hand with this the simple reproduction becomes gradually cyclical. It is just these intermediate steps between the two kinds of reproduction that make quite untenable the idea that the heterogeneous forms in cyclical propagation arise through so-called “heterogeneous generation,” _i.e._ through sudden _per saltum_ transformation. It is excusable if philosophers to whom these facts are strange, or who have to take the trouble of working them up, should adduce alternation of generation as an instance of “heterogeneous generation,” but by naturalists this should be once and for ever abandoned.

All other facts which have hitherto been referred to “heterogeneous generation” are still less explicable as such, inasmuch as they always relate to changes in single parts of an organism, such as the sudden change of fruit or flower in cultivated plants. The notion of _per saltum_ development, however, demands a total transformation--it comprises (as Von Hartmann quite correctly and logically admits) the idea of a _fixed specific type_ which can only be re-modelled _as a whole_, and cannot become modified piecemeal. It must further be added, that the observed variations which have arisen abruptly in single parts are not as a rule inherited:[308] fruit-trees are only propagated by grafting, _i.e._ by perpetuating the individual, and not by ordinary reproduction by seeds. Now, if we nowhere see sudden variations of large amount perpetuated by heredity, whilst we everywhere observe small variations which can all be inherited, must it not be concluded that _per saltum_ modification is not the means which Nature employs in transforming species, but that an accumulation of small variations takes place, these leading in time to large differences? Is it logical to reject the latter conclusion because our period of observation is too brief to enable us to directly follow long series of accumulations, whilst _per saltum_ variation is admitted, although unsupported by a single observation? As long as there remains any prospect of tracing large deviations to the continually observed phenomenon of small variations, I believe we have no right to resort to the purely hypothetical explanation afforded by _per saltum_ variations.

But the hypothesis of “heterogeneous generation” is not only without a basis of facts--it can also be directly shown to be untenable. Since the operation of an internal power of transformation does not explain adaptation to the conditions of life, the claims of natural selection to explain these transformations must be admitted; but the co-operation of a phyletic vital force and natural selection is inconceivable if we imagine the modifications to occur _per saltum_.

The supposed “heterogeneous generation” is always illustrated by the example of alternation of generation. The origination of a new animal form is thus conceived to take place in the same manner as we now see, in the cyclical reproduction of the Medusæ, free swimming, bell-shaped Medusoids, produced from fixed polypites, or _Cercariæ_ from Trematode worms by internal budding; in brief, it is imagined that one animal form suddenly gives rise to another widely deviating form by purely internal causes. Now on this theory it would be an unavoidable postulate, that by such a process of _per saltum_ development there arises not merely a new type of some species, but at the same time individuals capable of living and of persisting under, and fitted to, given conditions of life. But every naturalist who has attempted to completely explain the relation between structure and mode of life knows that even the small differences which separate one species from another, always comprise a number of minute structural deviations which are related to well defined conditions of life--he knows that in every species of animal the whole structure is adapted in the most exact manner _in every detail_ to special conditions of life. It is not an exaggeration when I say in every detail, since the so-called “purely morphological parts” could not be other than they are without causing changes in other parts which exercise a definite function. I will not indeed assert that in the most closely related species all the parts of the body must in some manner differ from one another, if only to a small extent; it seems to me not improbable, however, that an exact comparison would very frequently give this result. That animals which are so widely removed in their morphological relations as Medusæ and Polypes, or Trematoda and their “nurses,” are differently constructed in each of their parts can, however, be stated with certainty.

Now if this wide deviation in every part were in itself no obstacle to the assumption of a designing and re-modelling power, it would become so by the circumstance that all the parts of the organism must stand in the most precise relation to the external conditions of life, if the organism is to be capable of existing--all the parts must be exactly adapted to certain conditions of life. How can this be brought about by a transforming force acting spasmodically? Von Hartmann--who, in spite of his clear perception and widely extended scientific knowledge, cannot possibly possess a strong conviction of that harmony between structure and life-conditions prevailing throughout the whole system of the organism, and which personal research and contemplation are alone able to give--simply bridges over the difficulty by permitting natural selection to come to his aid as an “auxiliary principle” of the re-modelling power. It would not be supposed that naturalists would resort to the same device--nevertheless those who support the phyletic force and _per saltum_ development generally invoke natural selection as the principle which governs adaptation. But when does this agency come into operation? When by germinal metamorphosis a new form has arisen, this, from the first moment of its existence, must be adapted to the new conditions of life or it must perish. No time is allowed for it to continue in an unadapted state throughout a series of generations until adaptation is luckily reached through natural selection. Let us have either natural selection or a phyletic force--both together are inconceivable. If there exists a phyletic force, then it must itself bring about adaptation.

It might perhaps be here suggested that the same objection applies to that process of modification which is effected by small steps, but that it does so only when the change occurs suddenly. This, however, as I have already attempted to show, but very rarely takes place; in many cases (mimicry) the conditions even change in the first place through the change in form and therefore, as is evident, as gradually as the latter. It must be the same in all other cases where transformation of the existing form and not merely extinction of the species concerned takes place. The transmutation must always keep pace with the change in the conditions of life, since if the latter change more rapidly the species could not compete with rival species--it would become extinct.

The abrupt transformation of species implies sudden change in the conditions of life, since a Medusa does not live like a Polype, nor a Trematode like its “nurse.” For this reason it is impossible that natural selection can be an aiding principle of “heterogeneous generation.” If such abrupt transformation takes place it must produce the new form instantly equipped for the struggle for existence, and adapted in all its organs and systems of organs to the special conditions of its new life. But would not this be “pure magic”? It is not thereby even taken into consideration that here--as in the cases of mimicry--time and place must agree. The requirements of a pre-established harmony (“_prästabilirte Harmonie_”) further demand that an animal fitted for special conditions of life should only make its appearance at that precise period of the earth’s history when these special conditions are all fulfilled, and so forth.

But he who has learnt to perceive the numerous and fine relations which, in every species of animal, bring the details of structure into harmony with function, and who keeps in view the impelling power of these conditions, cannot possibly hold to the idea of a _per saltum_ development of animal forms. If development has taken place, it must have occurred gradually and by minute steps--in such a manner indeed that each modification had time to become equilibrated to the other parts, and in this way a succession of modifications gradually brought about the total transformation of the organism, and at the same time secured complete adaptation to new conditions of life.

Not only abrupt modification however, but every transformation is to be rejected when based upon the interference of a metaphysical principle of development. Those to whom the arguments already advanced against such a principle appear insufficient may once more be asked, how and where should this principle properly interfere? I am of opinion that one effect can have but one sufficient cause; if this suffices to produce it, no second cause is required. The hand of a watch necessarily turns once round in a circle in a given time as soon as the spring which sets the mechanism in movement is wound up; in an unwound watch a skilful finger can perhaps give the same movement to the hand, but it is impossible that the latter can receive both from the operator and from the spring at _the same time, the same motion_ as that which it would receive through either of these two powers _alone_. In the same manner it appears to me that the variations which lead to transformation cannot be at the same time determined by physical and by metaphysical causes, but must depend upon either one or the other.

On no side will it be disputed that at least one portion of the processes of organic life depends upon the mechanical co-operation of physical forces. How is it conceivable that sudden pauses should occur in the course of these causal forces, and that a directive power should be substituted therefor, the latter subsequently making way again for the physical forces? To me this is as inconceivable as the idea that lightning is the electric discharge of a thunder-cloud, of which the formation and electrical tension depends upon causal forces, and of which the time and place are purely determined by such forces, but that Jupiter has it nevertheless in his power to direct the lightning flash according to his will on to the head of the guilty.

Now although I deny the possibility or conceivability of the contemporaneous co-operation of teleological and of causal forces in producing any effect, and although I maintain that a purely mechanical conception of the processes of nature is alone justifiable, I nevertheless believe that there is no occasion for this reason to renounce the existence of, or to disown, a directive power; only we must not imagine this to interfere directly in the mechanism of the universe, but to be rather behind the latter as the final cause of this mechanism.

Von Baer himself points this out to us, although he does not follow up the complete consequences of his arguments. He especially insists in his book, which abounds in beautiful and grand ideas, that the notions of necessity (causality) and of purpose by no means necessarily exclude one another, but rather that they can be connected together in a certain manner. Thus, the watchmaker attains his end, the watch, by combining the elastic force of a spring with wheel-work, _i.e._ by utilizing physical necessities; the farmer accomplishes his purpose, that of obtaining a crop of corn, by sowing the seed in suitable land, but the seed must germinate as an absolute necessity when exposed to the influences of warmth, soil, moisture, &c. Thus, in these instances a chain of necessities is undoubtedly connected with a teleological force, the human will; and it directly follows from such cases that wherever we see an aim or result attained through necessities, the directive force does not interrupt the course of the series of necessities which have already commenced, but is active before the first commencement of these necessities, since it combines and sets the latter in movement. From the moment when the mechanism of the watch is combined harmoniously and the spring wound up, it goes without the further interference of the watchmaker, just as the corn-seed when once placed in the earth develops into a plant without assistance from the farmer.

If we apply this argument to the development of the organic world, those who defend mechanical development will not be compelled to deny a teleological power, only they would have with Kant[309] to think of the latter in the only way in which it can be conceived, viz. _as a Final Cause_.

In the region of inorganic nature nobody any longer doubts the purely mechanical connection of the phenomena. Sunshine and rain do not now appear to us to be whims of a deity, but divine natural laws. As the knowledge of the processes of nature advances, the point where the divine power designedly interrupts these processes must be removed further back; or, as the author of the criticism of the philosophy of the Unconscious[310] expresses it, all advance in the knowledge of natural processes depends “upon the continual elimination of the idea of the miraculous.” We now believe that organic nature must be conceived as mechanical. But does it thereby follow that we must totally deny a final Universal Cause? Certainly not; it would be a great delusion if any one were to believe that he had arrived at a comprehension of the universe by tracing the phenomena of nature to mechanical principles. He would thereby forget that the assumption of eternal matter with its eternal laws by no means satisfies our intellectual need for causality. We require before everything an explanation of the fact that relationships everywhere exist between the parts of the universe--that atoms everywhere act upon one another.[311] He who can content himself with the assumption of matter may do so, but he will not be able to show that the assumption of a Universal Cause underlying the laws of nature is erroneous.

It will not be said that there is no advantage in assuming such a Final Cause, because we cannot conceive it, and indeed cannot so much as demonstrate it with certainty. It certainly lies beyond our power of conception, in the obscure region of metaphysics, and all attempts to approach it have never led to anything but an image or a formula. Nevertheless there is an advance in knowledge in the assumption of this Cause which well admits of comparison with those advances which have been led to by certain results of the new physiology of the senses. We now know that the images which give us our sense of the external world are not “actual representations having any degree of resemblance,”[312] but are only signs for certain qualities of the outer world, which do not exist as such in the latter, but belong entirely to our consciousness. Thus we know for certain that the world is not as we perceive it--that we cannot perceive “things in their essence”--and that the reality will always remain transcendental to us. But who will deny that in this knowledge there is a considerable advance, in spite of its being for the most part of a negative character? But just as we must assume behind the phenomenal world of our senses an actual world of the true nature of which we receive only an incomplete knowledge (_i.e._ a knowledge corresponding only in reality with the relations of time and space), so behind the co-operating forces of nature which “aim at a purpose” must we admit a Cause, which is no less inconceivable in its nature, and of which we can only say one thing with certainty, viz., that it must be teleological. Just as the former first leads us to perceive the true value of our sensual impressions, so does the latter knowledge lead us to foresee the true significance of the mechanism of the universe.

It is true that in neither case do we learn more than that there is something present which we do not perceive, but in both instances this knowledge is of the greatest value. The consciousness that behind that mechanism of the universe which is alone comprehensible to us there still lies an incomprehensible teleological Universal Cause, necessitates quite a different conception of the universe--a conception absolutely opposed to that of the materialist. Most correctly and beautifully does Von Baer say that “a purpose cannot be otherwise conceived by us than as proceeding from a will and consciousness; in this would the ‘aiming at a purpose,’ which appears to us as reasonable as it is necessary, have its deepest root.” If we conceive in this world a divine Universal Power exercising volition as the ultimate basis of matter and of the natural laws resident therein, we thus reconcile the apparent contradiction between the mechanical conception and teleology. In the same way that Von Hartmann, somewhere speaks of the immanent teleology of a machine, we might speak of the immanent teleology of the universe, because the single forces of matter are so exactly adjusted that they must give rise to the projected world, just as the wheels and levers of a machine bring forth a required manufactured article. I admit that these are grossly anthropomorphic ideas. But as mortals can we have any other ideas? Is not the notion of purpose in itself an equally anthropomorphic one? and is there any certainty that the idea of causality is less so? Do we know that causality is unlimited, or that it is universally valid? In the absence of this knowledge, should it not be permissible to satisfy as far as we can the craving of the human mind for a spiritual First Cause of the universe, by speaking of it in terms conceivable to human understanding? We can take up such a final position and still be conscious that we thereby form no certain conception, and indeed come no nearer to the reality. The materialist still makes use of the notion of “eternity,” and frequently handles it as though it were a perfectly known quantity. We nevertheless do not seriously believe that by the expression “eternal matter,” any true idea resulting from human experience is gained.

If it is asked, however, how that which in ourselves and in the remainder of the animal world is _intellectual_ and _perceptive_, which _thinks_ and _wills_, is ascribable to a mechanical process of organic development--whether the development of the mind can be conceived as resulting from purely mechanical laws? I answer unhesitatingly in the affirmative with the pure materialist, although I do not agree with him as to the manner in which he derives these phenomena from matter, since thinking and extension are heterogeneous things, and one cannot be considered as a product of the other. But why should not the ancient notion of “conscious matter” given out by Maupertuis and Robinet, not be again entertained, as pointed out in recent times by Fechner?[313] Would there not thus be found a useful formula for explaining phenomena hitherto quite incomprehensible?

Von Hartmann in criticizing himself, designates the sensibility of atoms as an “almost inevitable hypothesis” (p. 62), “inevitable because if sensibility were not a general and original property of the constituent elements of matter, it would be absolutely incomprehensible how through its potentiality and integration that sensibility known to us as being possessed by the organism could have arisen.” “It is impossible that from purely external elements devoid of all internality (_Innerlichkeit_) there should suddenly appear, by a certain mode of combination, an internality which becomes more and more richly developed. The more certainly science becomes convinced that in the sphere of externality (_Äusserlichkeit_) the higher (organic) phenomena are only results of combination, or are the aggregate phenomena of the elementary atomic forces, the more surely, when she once seriously concerns herself with this other question, will she not fail to be convinced that the sensibility possessed by higher stages of consciousness can be only combination-results, or the aggregate phenomena of the elementary sensations of atoms, although these atomic sensations as such always remain below the level of the higher combinations of consciousness.” In confusing this double-sided nature of the objective phenomenon “lies the main error of all materialism and of all subjective idealism. Just as the attempt of the latter (subjective idealism) to construct the external phenomena of existence in space out of functions of internality and their combinations is impossible, so is the endeavour of the former (materialism) to build up internal sensation out of any combinations of force acting externally in space equally impossible.”

I have no intention of going any deeper into these questions. I mention them only in order to point out that even from this side there appears to me no obstacle in the way of a purely mechanical conception of the processes of the universe. The naturalist may be excused if he attempts to penetrate into the region of philosophy; it arises from the wish to be able to contribute a little towards the reconciliation of the latest knowledge of the naturalist with the religious wants of the human mind--towards the aim striven for by both sides, viz. a satisfactory and harmonious view of the universe, according with the state of knowledge of our time.

I believe that I have shown that the theory of selection by no means leads--as is always assumed--to the denial of a teleological Universal Cause and to materialism, and I thereby hope that I have cleared the way for this doctrine, the importance of which it is scarcely possible to over-estimate. Many, and not the most ill-informed, do not get so far as to make an unbiassed examination into the facts, because they are at the outset alarmed by the to them inevitable consequence of the materialistic conception of the universe. Mechanism and teleology do not exclude one another, they are rather in mutual agreement. Without teleology there would be no mechanism, but only a confusion of crude forces; and without mechanism there would be no teleology, for how could the latter otherwise effect its purpose?[314]

Von Hartmann correctly says:--“The most complete mechanism conceivable is likewise the most completely conceivable teleology.” We may thus represent the phenomenal universe as such a completely conceivable mechanism. With this conception vanish all apprehensions that the new views would cause man to lose the best that he possesses--morality and purely human spiritual culture. He who, with Von Baer, considers the laws of nature as the “permanent expressions of the will of a creative principle,” will clearly perceive that a further advance in the knowledge of these laws need not divert man from the path of increasing improvement, but must further him in this course--that the knowledge of truth, whatever may be its purport, cannot possibly be considered a backward step. Let us take our stand boldly on the ground of new knowledge, and accept the direct consequences thereof, and we shall not be obliged to give up either morality or the comforting conviction of being part of an harmonious world, as a necessary member capable of development and perfection.

Any other mode of interference by a directive teleological power in the processes of the universe than by the appointment of the forces producing them, is however, at least to the naturalist, inadmissible. We are still far removed from completely understanding the mechanism by means of which the organic world is evoked--we still find ourselves at the very beginning of knowledge. We are, however, already convinced that both the organic and the inorganic worlds are dependent only upon mechanical forces, for to this conclusion we are led, not only by the results of investigators who have restricted themselves to limited provinces, but also by the most general considerations. But although the force of these arguments may not be acknowledged, and although one might maintain that the inductional proofs against the existence of a “phyletic vital force” have been directed only against points of detail, or have never been completely demonstrated, _i.e._ for all points, it must nevertheless be conceded, that for the naturalist the mechanical conception of Nature is the only one possible--that he is not at all justified in abandoning this view so long as the interference of teleological forces _in the course_ of the processes of organic development has not been demonstrated to him. Thus, it will not be immaterial whether a conception of Nature which to many seems inevitable is consistent with the idea of universal design, or a final directive universal principle, since the value which we may attach to our own lives and aims, essentially depends thereon. The final and main result of this essay will thus be found in the attempted demonstration that the mechanical conception of Nature very well admits of being united with a teleological conception of the Universe.

THE END.

FOOTNOTES

[171] [The slight variability in the colour of this pupa, opens up the interesting question of the photographic sensitiveness of this and other species, which is stated to cause them to assimilate in colour to the surface on which the larva undergoes its final ecdysis. Some experiments upon this subject have been recorded by Mr. T. W. Wood, Proc. Ent. Soc. 1867, p. xcix, but the field is still almost unexplored. R.M.]

[172] “Über den Einfluss der Isolirung auf die Artbildung.” Leipzig, 1872, p. 20.

[173] In some instances _Deilephila Lineata_ has also been seen by day hovering over flowers.

[174] It is true that I only reared one brood, but from this fifty specimens were obtained. It would be interesting to know whether this variety of the caterpillar is distributed over the whole of Southern Europe.

[175] In this sense Lubbock says:--“It is evident that creatures which, like the majority of insects, live during the successive periods of their existence in very different circumstances, may undergo considerable changes in their larval organization in consequence of forces acting on them while in that condition; not, indeed, without affecting, _but certainly without affecting to any corresponding extent_, their ultimate form.”--“Origin and Metamorphoses of Insects,” London, 1874, p. 39.

[176] “Grundzüge der Zoologie,” 1875.

[177] [Lepidopterists are of course aware that even these distinctions are not absolute, as no single character can be named which does not also appear in certain moths. The definition in this case, as in that of most other groups of animals and plants, is only a general one. See, for instance, Westwood’s “Introduction to the Classification of Insects,” vol. ii. pp. 330-332. Also some remarks by C. V. Riley in his “Eighth Annual Report” on the insects of Missouri, 1876, p. 170. With reference to the antennæ as a distinguishing character, see Mr. A. G. Butler’s article in “Science for All,” 1880, part xxvii. p. 65. R.M.]

[178] The genus of _Morphinæ, Discophora_, possesses hairs very similar to those of the genus _Cnethocampa_ belonging to the _Bombycidæ_.

[179] [The larvæ of genera 14, _Phyciodes_, and 35, _Crenis_, are likewise spiny. See Edwards’ “Butt. of N. Amer.” vol. ii. for figures of the caterpillar of _Phyc. Tharos_: for notes on the larvæ of _Crenis Natalensis_ and _C. Boisduvali_ see a paper by W. D. Gooch, “Entomologist,” vol. xiv. p. 36. The larvæ of genus 55, _Ageronia_, are also spiny. (See Burmeister’s figure of _A. Arethusa_, “Lép. Rép. Arg.” Pl. V. Fig. 4). The larvæ of genus 98, _Aganisthos_, also appear to be somewhat spiny (see Burmeister’s figure of _A. Orion_, _loc. cit._ Pl. V. Fig. 6), and this raises the question as to whether the genus is correctly located in its present position. The larvæ of the following genera figured in Moore’s “Lepidoptera of Ceylon,” parts i. and ii., are all spiny:--6, _Cirrochroa_ (Pl. XXXII.); 7, _Cynthia_ (Pl. XXVI.); 27, _Kallima_ (Pl. XIX.); and 74, _Parthenos_ (Pl. XXIV.). Many species of caterpillars which are spiny when adult appear to be spineless, or only slightly hairy when young. See Edwards’ figures of _Melitæa Phaeton_, _Argynnis Diana_, and _Phyc. Tharos_ (_loc. cit._) and his description of the larva of _Arg. Cybele_, “Canad. Entom.” vol. xii. p. 141. The spiny covering thus appears to be a character acquired at a comparatively recent period in the phyletic development. R.M.]

[180] [The larvæ of the 110th genus, _Paphia_, Fabr. (_Anæa_, Hübn.) are also smoothed-skinned. See Edwards’ figure (_loc. cit._ vol. i. Pl. XLVI.) of _P. Glycerium_. Also C. V. Riley’s “Second Annual Report” on the insects of Missouri, 1870, p. 125. Burmeister figures the larva of a species of _Prepona_ (genus 99) which is smooth (_P. Demophon_, _loc. cit._ Pl. V. Fig. 1). The horns on the head of _Apatura_, &c., may possibly be a survival from a former spiny condition. R.M.]

[181] “Synopsis of the described Lepidoptera of North America.” Washington, 1862.

[182] “Catalog der Lepidopteren des Europäischen Faunengebietes.” Dresden, 1871.

[183] This group of moths (“Schwärmer”) is regarded as of very different extents by systematists; when I here comprise under it only the _Sphingidæ_ proper and the _Sesiidæ_, I by no means ignore the grounds which favour a greater extension of the group; the latter is not rigidly limited. [The affinities of the _Sesiidæ_ (_Ægeriidæ_) are by no means clearly made out: it appears probable that they are not related to the _Sphingidæ_. See note 160, p. 370. R.M.]

[184] [For Mr. A. G. Butler’s observations on the genus _Acronycta_, see “Trans. Ent. Soc.” 1879, p. 313; and note 68, p. 169, of the present volume. R.M.]

[185] [The following characters are given in Stainton’s “Manual of British Butterflies and Moths,” vol. i. p. 114:--“Larva of very variable form: at one extreme we find the singular _Cerura_ larvæ, with only fourteen legs, and two long projecting tails from the last segment; at the other extreme we have larvæ with sixteen legs and no peculiarity of form, such as _Chaonia_ and _Bucephala_; most have, however, the peculiarity of holding the hind segment of the body erect when in repose; generally quite naked, though downy in _Bucephala_ and rather hairy in _Curtulu_; very frequently there are projections on the back of the twelfth segment.” R.M.]

[186] Encyl. Meth. ix. p. 310.

[187] [The genus _Vanessa_ (in the wide sense) appears to be in a remarkable condition of what may be called phyletic preservation. Thus, the group of species allied to _V. C.-album_ passes by almost insensible steps into the group of butterflies typified by our “Tortoiseshells.” The following is a list of some of the intermediate species in their transitional order:--_I.-album_, _V.-album_, _Faunus_, _Comma_, _California_, _Dryas_, _Polychloros_, _Xanthomelas_, _Cashmirensis_, _Urticæ_, _Milberti_, &c. Similarly, our _Atalanta_ and _Cardui_ are connected by a number of intermediate forms, showing a complete transition from the one to the other. The following is the order of the species so far as I am acquainted with them:--_Atalanta_, _Dejeanii_, _Callirhoë_, _Tammeamea_, _Myrinna_, _Huntera_, _Terpsichore_, _Carye_, _Kershawii_, and _Cardui_. R.M.]

[188] “Prodromus Systematis Lepidopterorum.” Regensburg, 1864.

[189] [The larva of _Acherontia Morta_, figured by Butler (see note 121, p. 262), possesses the characteristically recurved horn; that of _Ach. Medusa_ figured by the same author, does not appear to possess this character in any marked degree. R.M.]

[190] [See note 97, p. 233. R.M.]

[191] _Loc. cit._ Pl. XXV. [This species is referred by Butler to the genus _Paonias_, Hübn. R.M.]

[192] Abbot and Smith, Pl. XXIX. [Placed by Butler in the genus _Cressonia_, Grote and Robinson. Abbot and Smith state that this larva is sometimes green. According to Mr. Herman Strecker (Lepidop. Rhopal. and Hetero, Reading, Pa. 1874, p. 54) it feeds upon black walnut (_Juglans Nigra_), hickory (_Carya Alba_), and ironwood (_Ostrya Virginica_). Of the North American species of _Smerinthus_, the following, in addition to _Excæcatus_, closely resemble our _Ocellatus_:--_S. (Calasymbolus) Geminatus_, Say; _(C.) Cerisii_, Kirby; and _Ophthalmicus_, Boisd. In addition to _S. (Cressonia) Juglandis_, _S. (Triptogon) Modesta_ much resembles our _Populi_. The larva of _Geminatus_, according to Strecker, is “pale green, lightest above, with yellow lateral granulated stripes; caudal horn violet; stigmata red. It feeds on the willow.” R.M.]

[193] Cat. Brit. Mus.

[194] [This lengthening of the true legs is mimetic according to Hermann Müller, and causes the anterior portion of the caterpillar to resemble a spider. See note 129, p. 290. R.M.]

[195] [Certain butterflies appear to be crepuscular, if not nocturnal in their habits. Thus in his “Notes on the Lepidoptera of Natal,” Mr. W. D. Gooch states that he never saw _Melanitis_, _Leda_, or _Gnophodes Parmeno_ on the wing by day, but generally during the hour after sunset. He adds:--“My sugar always attracted them freely, even up to 10 or 11 p.m.” Many species of _Hesperidæ_ are also stated to be of crepuscular habits by this same observer. See “Entomologist,” vol xvi. pp. 38 and 40. R.M.]

[196] I only make this assumption for the sake of simplicity, and not because I am convinced that the existing _Rhopalocera_ are actually the oldest Lepidopterous group.

[197] Zeitschrift für wissenschaftl. Zoologie, vol. xx. p. 519.

[198] [See for instance Lubbock’s “Origin and Metamorphoses of Insects,” chap. iii.; and F. M. Balfour’s “Comparative Embryology,” vol. i., 1880, pp. 327--356. This last work contains an admirable _résumé_ of our knowledge of the embryonic development of insects up to the date of publication. R.M.]

[199] Are not the 4th, 11th, and 12th segments destitute of the rudiments of legs as in the larvæ of all existing saw-flies? I might almost infer this from Bütschli’s figures (see for instance Pl. XXV., Fig. 17A).

[200] [The grub-formed Hymenopterous larvæ, like the larvæ of all other holometabolous insects, thus represent an acquired degenerative stage in the development, _i.e._ an adaptation to the conditions of life at that stage. Bearing in mind the above-quoted observations of Bütschli and the caterpillar-like form of the Terebrantiate group of Hymenopterous larvæ, the following remarks of Balfour’s (_loc. cit._ p. 353), appear highly suggestive:--“While in a general way it is clear that the larval forms of insects cannot be expected to throw much light on the nature of insect ancestors, it does nevertheless appear to me probable that such forms as the caterpillars of the Lepidoptera are not without a meaning in this respect. It is easy to conceive that even a secondary larval form may have been produced by the prolongation of one of the embryonic stages; and the general similarity of a caterpillar to _Peripatus_, and the retention by it of post-thoracic appendages, are facts which appear to favour this view of the origin of the caterpillar form.” See also Sir John Lubbock, _loc. cit._, pp. 93 and 95. R.M.]

[201] [In the most recent works dealing with this order six groups, based on the character of the imagines are recognized, viz.:--_Tubulifera_, _Terebrantia_, _Pupivora_, _Heterogyna Fossores_, and _Mellifera_. (See, for instance, F. P. Pascoe’s “Zoological Classification,” 2nd ed. p. 147.) Of these groups the larvæ of the _Terebrantia_ as thus restricted are all of the caterpillar type (_Tenthredinidæ_ and _Siricidæ_), whilst those of the other groups are maggot-shaped. For a description of the development of the remarkable aberrant larva of _Platygaster_, see Ganin in Zeit. f. wissenschaftl. Zool., vol. xix. 1869. R.M.]

[202] [For recent investigations on the structure of the thorax in Diptera, see a paper by Mr. A. Hammond, in Journ. Linn. Soc., Zoology, vol xv. p. 9. R.M.]

[203] I am familiar with the fact that the two sub-orders of true Diptera, the short-horned (_Brachycera_), and the long-horned (_Nemocera_), are not sharply limited; and I am likewise well acquainted with the circumstance that there are forms which connect the two larval types. The connecting forms of the imagines do not, however, always coincide with the intermediate larval forms, so that there here arises a second and very striking incongruence of morphological relationship which depends only upon the circumstance that the one stage has diverged in form more widely than the other through a greater divergence in the conditions of life. The difficulty is in these cases aggravated because an apparent is added to the true form-relationship through convergence, so that without going into exact details the form and genealogical relationships of the Diptera cannot be distinguished. It would be of great interest for other reasons to make this investigation, and I hope to be able to find leisure for this purpose at some future period.

[204] “Entwicklung der Dipteren.” Leipzig, 1864.

[205] Lubbock concludes from the presence of thoracic legs in the embryonic larva of bees that these have been derived from a larva of the _Campodea_ type, but he overlooks the fact that the rudiments of the abdominal legs are also present; _loc. cit._, p. 28.

[206] “Für Darwin,” Leipzig, 1864, p. 8.

[207] Mem. Peabody Acad. of Science, vol. i. No. 3.

[208] Verhandl. Wien. Zoolog. Botan. Gesellsch. 1869, p. 310.

[209] Über Ontogenie und Phylogenie der Insekten. Eine akademische Preisschrift. Jen. Zeitschrift. Bd. x. Neue Folge, iii. Heft 2. 1876. [Some remarks by F. M. Balfour on the origin of certain larval forms have already been quoted in a previous note (p. 485). This author further states:--“The fact that in a majority of instances it is possible to trace an intimate connection between the surroundings of a larva and its organization proves in the clearest way _that the characters of the majority of existing larval forms of insects have owed their origin to secondary adaptations_. A few instances will illustrate this point:--In the simplest types of metamorphosis, _e.g._ those of the Orthoptera genuina, the larva has precisely the same habits as the adult. We find that a caterpillar form is assumed by phytophagous larvæ amongst the Lepidoptera, Hymenoptera, and Coleoptera. Where the larva has not to go in search of its nutriment the grub-like apodous form is assumed. The existence of such an apodous larva is especially striking in the Hymenoptera, in that rudiments of thoracic and abdominal appendages are present in the embryo and disappear again in the larva.... It follows from the above that the development of such forms as the Orthoptera genuina is more primitive than that of the holometabolous forms, &c.” Comparative Embryology, vol. 1, p. 352. R.M.]

[210] [The _Aphaniptera_ are now recognized in this country as a sub-order of Diptera. See, for instance, Huxley’s “Anatomy of Invertebrated Animals,” p. 425, and Pascoe’s “Zoological Classification,” 2nd ed. p. 122. R.M.]

[211] [This illustration of course only applies to the old arrangement of the Hymenoptera into _Terebrantia_ and _Aculeata_. See also note 201, p. 488. R.M.]

[212] [Eng. ed. This law is perhaps a little too restricted, inasmuch as it is theoretically conceivable that the organism may be able to adapt itself to similar conditions of life in different ways; differences of form could thus depend sometimes upon differences of adaptation and not upon differences in the conditions of life, or, as I have formerly expressed it, it is not necessary to allow always only _one_ best mode of adaptation.]

[213] [It must be understood that the word rendered here and elsewhere throughout this work as “transformation” is not to be taken in the narrow sense of metamorphosis, but as having the much broader meaning of a change of any kind incurred by an organism. Metamorphosis is in fact but one phase of transformation. R.M.]

[214] By the Editor.

[215] Mr. C. V. Riley in his excellent “Annual Reports” already quoted in previous notes, states that the larvæ of _Agrotis Inermis_, _Leucania Unipuncta_ (Army-worm), and _L. Albilinea_ are all loopers when newly hatched. (See First Report, p. 73; Eighth Report, p. 184; and Ninth Report, p. 53.)

[216] The following species not referred to in the previous part of this work are figured by Semper (Beit. zur Entwicklungsgeschichte einiger ostasiat. Schmet.; Verhandl. d. k.k. zoo. bot. Gesell. in Wien, 1867):--_Panacra Scapularis_, Walk.; _Chærocampa Clotho_, Drury; and _Diludia (Macrosila) Discistriga_, Walk. The following are figured by Boisduval and Guenée. (Spéc. Gén. 1874):--_Smerinthus Ophthalmicus_, Boisd.; _Sphinx Jasminearum_, Boisd.; _S. (Hyloicus) Plebeia_, Fabr.; _S. (Hyloicus) Cupressi_, Boisd.; _S. (Pseudosphinx) Catalpæ_, Boisd.; _Philampelus Jussiuæ_, Hübn. (= _Sphinx Vitis_, Linn.?); and _Ceratomia Amyntor_, Hübn. As the works of Abbot and Smith, and Horsfield and Moore have been exhausted by Dr. Weismann, it is quite unnecessary to extend this note by giving a list of the species figured by these authors.

[217] The same inference has already been drawn with respect to _Pterogon (Proserpinus) Œnotheræ_, see pp. 257, 258.

[218] This would of course be the _fourth_ segment if the head be considered the first, as on the Continent.

[219] “Second Annual Report,” 1870, p. 78.

[220] “Entomologist,” vol. xiv. p. 7.

[221] With reference to the habits of _C. Capensis_ (p. 531), I have since been informed by Mr. Trimen that this species does not conceal itself by day, so that the dimorphism may be regarded as a character retained from an earlier period and adapted to the present life conditions.

[222] “Kosmos,” Dec. 1877, p. 218. The paper is here introduced chiefly with a view to illustrate an important case of incongruence among Lepidopterous pupæ.

[223] [Maracujá, the local name for the Passiflora. R.M.]

[224] See p. 448.

[225] Verhandl. Schweiz. Naturforsch. Gesellschaft. Einsiedeln, 1868.

[226] [Eng. ed. In 1878 Señor José M. Velasco published a paper entitled “Description, metamorfosis. y costumbres de una especie nueva del genero _Siredon_.” Memor. Sociedad Mexicana de Historia Natural, December 26th. See Addendum to this essay.]

[227] Dana and Silliman’s Amer. Journ., 3rd series, i. p. 89. Annals Nat. Hist. vii. p. 246.

[228] Proc. Zoo. Soc. 1870, p. 160.

[229] Compt. Rend., vol. lx. p. 765 (1865).

[230] Nouvelles Archives du Muséum d’Histoire Nat. Paris, 1866, vol. ii. p. 268.

[231] Proc. Boston Soc., vol. xii. p. 97; Silliman’s Amer. Journ., vol. xlvi. p. 364; reference given in “Troschel’s Jahresbericht” for 1868, p. 37.

[232] Proc. Boston Soc., vol. xii. p. 97; Silliman’s Amer. Journ., vol. xlvi. p. 364. I have not been able to get a copy of this paper, and quote from a reference in “Troschel’s Jahresbericht.” See preceding note.

[233] Dana and Silliman’s Amer. Journ. See note 3.

[234] Proc. Acad. Philadelph. xix. 1867, pp. 166-209.

[235] Mém. Acad. Petersb. vol. xvi.

[236] [Eng. ed. Seidlitz is an exception, since in his work on Parthenogenesis (Leipzig, 1872, p. 13) he states that “In the Axolotl, Pædogenesis, which is not in this case ... monogamous, but sexual, and indeed gynækogenetic, has already become so far constant that it has perhaps entirely superseded the orthogenetic reproduction.”]

[237] Über den Einfluss der Isolirung auf die Artbildung. Leipzig, 1872, p. 33.

[238] Duméril represents the teeth of the _vomer_ as separated from those of the _os palatinum_ by a gap. This is probably accidental, since Gegenbaur (Friedrich u. Gegenbaur, the skull of Axolotl, Würzburg, 1849) figures the rows of teeth as passing over from the one bone to the other without interruption. This was the case with the Axolotls which I have been able to examine on this point; but this small discrepancy is, however, quite immaterial to the question here under consideration.

[239] See O. Hertwig “Über das Zahnsystem der Amphibien und seine Bedeutung für die Genese des Skelets der Mundhöhle.” Archiv. für microsc. Anat., vol. xi. Supplement, 1874.

[240] [Eng. ed. These Amblystomas have since died and have been minutely described by Dr. Wiedersheim. See his memoir, “Zur Anatomie des _Amblystoma Weismanni_,” in Zeit. für wiss. Zool., vol. xxxii. p. 216.]

[241] See Strauch, _loc. cit._ p. 10.

[242] See Part I. of this volume.

[243] [This is the principle of “Degeneration” recognized by Darwin (see “Origin of Species,” 6th ed. p. 389, and “Descent of Man,” vol. i. p. 206), and given fuller expression to by Dr. Anton Dohrn (see his work entitled “Der Ursprung der Wirbelthiere und das Princip des Functionswechsels.” Leipzig, 1875). A large number of cases have been brought together by Prof. E. R. Lankester, in his recent interesting work on “Degeneration, a Chapter in Darwinism.” Nature series, 1880. R.M.]

[244] “Sulla Larva del _Triton Alpestris_.” Archivio per la Zoologia. Genova e Torino, 1861, vol. i. pp. 206-211.

[245] See also Lubbock “On the Origin and Metamorphoses of Insects,” London, 1874.

[246] See the first essay “On the Seasonal Dimorphism of Butterflies,” p. 82.