[BF] Referring to organized being.
[BG] _Origin of Species_, p. 577.
[BH] _Doct. of Descent_, p. 161-2.
[BI] _Origin of Species_, 4th ed. p. 143.
[BJ] _Doct. of Descent_, 162.
[BK] _Origin of Species_, 4th ed. p. 141.
[BL] It may be well to mention here that the _third_ American edition is from the _fifth_ English edition.
[BM] _Origin of Species_, 6th ed., p. 289.
[BN] _Origin of Species_, 6th. ed. chap. iv. p. 100.
[BO] _Contributions to the Natural History of the United States_, Introduction, Boston, 1857; and _Essay on Cla.s.sification_, p. 15, published separately; London, 1859. See Appendix VI.
[BP] _Origin_, 4th ed. p. 143.
[BQ] _Origin of Species_, 6th. ed. chap. iv. p. 100.
LECTURE V.
RELATIONS OF LOWER AND HIGHER ORGANISMS.
From the general aspects of the theory of species, we pa.s.s to the consideration of distinct groups of organism, with the view of ascertaining their relations to each other. In doing so, it is better to begin at the lower end of the scale, leaving for a more advanced stage of inquiry the higher types of organism. In this department of the subject, special obligations are due to the wide range of investigations either occasioned or stimulated by the theory of evolution. For, whatever may be the ultimate award pa.s.sed on this theory, there will be a unanimous recognition of the great value to science attending on the varied forms of inquiry stimulated by the writings of Mr. Charles Darwin. And one obvious and strong reason for such acknowledgment is that so many of the results of these researches have an inherent value quite distinct from their testimony in favor of the theory that the struggle for existence is the princ.i.p.al factor in the origin of new species.
One of the most interesting fields of observation thus opened, is that concerned with the fertilization of plants by the intervention of insects and birds. A beginning in this department was made by the German naturalist, Christian Konrad Sprengel, who published in 1793 the report of his observations. In this he has been followed by Darwin, in 1862; by Dr. Hooker, Professor Asa Gray whose contributions appeared in the _American Journal of Science and Art_ in 1862, and 1863, Moggridge, Fritz Muller, and Sir John Lubbock. The facts now acc.u.mulated, rank as an important contribution to botany and zoology, and naturally fall within the circle of recent advances to which it is desirable that attention be turned.
The general result is one of great interest, as ill.u.s.trating a striking degree of interdependence between lower and higher organisms,--the vegetable and animal kingdom contributing to each other"s subsistence and propagation. Flowers present special attractions to insects flying around, alluring them by varied colors, and providing for them by secreting stores of honey; on the other hand, these insects (flies, bees, wasps, etc.), seeking the honey which satisfies their wants, at the same time carry the pollen from one flower to another, thus providing for the fertilizing of the plants. In some cases, fertilization is secured by a natural process within the organism itself; in other cases, the pollen is scattered over a region by the wind; but the most wonderful, and at the same time efficient mode of providing for the growth of vigorous plants, is fertilization by the agency of insect life.
A brief outline of the ordinary structure of the flower will introduce to a ready appreciation of the scientific interest attaching to this last mode of fertilization, both as concerning the functions of different portions of the flowers, and the relation of dependence established between higher and lower forms of organism, so that each is dependent on the other.
Every flower as it unfolds from the bud, consists of a series of whorls, or layers of substance twined or twirled round in such a manner as to unfold or coil back, as the flower opens. The _outermost_ of these whorls (_calyx_) is a mere covering or sheath, usually of a green color, which protects the bud during the more tender period, curling up and withering as the flower opens, spreading forth its beauty. The _second_ whorl (_corolla_) is what we more commonly regard as the flower proper, the colored leaves, or cup, or bell, according to the specific shape distinguishing the plant. The _third_ whorl consists of a series of stalks or filaments (_stamens_) which as the flower matures or ripens stand up distinct from each other, each one having at its summit a little tuft or cushion (_anther_) covered with a fine dust or powder (_pollen_). The _fourth_ or inner-most whorl, the centre piece of the flower (_pistil_) is that in which the seed is generated and brought to maturity. We may thus say of the flower, that its outermost whorl is a temporary covering which withers and shrinks out of view, when the beauty of the inner structure is laid open; that the second is that which attracts the eye by the loveliness of its hues; while the two which belong to the internal structure of the flower are concerned with the reproduction or propagation of the plant, providing for the healthy germ from which a fresh plant of the same order may spring up. The relation of the fine yellow powder produced at the tips of the third whorl, to the seeds which are gathered together within the fourth whorl, is the matter to which special attention has been directed by the recent discoveries which have rewarded patient research. The fine powder or pollen needs to be carried to the seed, so that its properties may operate upon that seed, if it is to be fertilized, or so matured, as to fulfil its function in generating a new plant when it is committed to the soil. In many cases it is enough that the fine powder should fall down from its elevation on the seeds below. This is self-fertilization, and is easily provided for by the mere bending of the head of the flower as it approaches maturity, or by the swaying of it in the breeze. But a more difficult, and as we might be inclined to add, more precarious, because less certain, method for fertilization is required in many cases. The experiments carried on by all our gardeners, and in a still more extended scale in all our centres of botanic research, have established the fact that in many cases, the yellow powder of one plant must be in some manner carried over to the seed produced within another flower, if that seed is to yield a satisfactory result to the horticulturist.
We have thus two prominent facts here. The one is _the essential importance of the pollen_ for fertilization; and the other, _the need for the transference of the pollen_ from one plant to another in order to secure reproduction of vigorous growth by the sowing of the seed. As to the first, the pollen, which appears a fine powder or flour contains fluid protoplasm, that which Professor Huxley has described as the "single physical basis of life under all the diversities of vital existence."[BR] These pollen grains falling on the seed discharge their protoplasmic fluid upon it, and by this means contribute to fertilization. This original or primordial form of vitalising agency is carried from one part of the flower to another, and this transference is the law regulating the propagation of flowering plants.
But, just at this point, we come upon the most striking results of recent research. Though all pollen is of this primary nature, named protoplasm, it is not found to hold true that pollen is of the same value for fertilization from whatever quarter it comes. On the contrary, most important differences result according to the source of the pollen. There is first the process of self-fertilization. But in many cases,--Mr. Darwin has shown that this holds of the majority of the orchids,--transference of the pollen from one plant to another proves to be a great advantage, if not an actual necessity for propagation of the plant. This process, known as cross-fertilization, gives a healthy and vigorous growth; want of it, will lead to degeneration, and ultimate extinction. This discovery has introduced a whole series of the most striking observations, throwing a flood of light on the distribution and interdependence of distinct forms of organism. The necessary relation between the pollen and the seed having been acknowledged, and next the value of transference of pollen from one plant to another, the first step in the line of discovery was made by the observation of a natural provision to _prevent self-fertilization_ by rendering it impossible that the pollen of a plant should fall on the seed of that plant. This entrance on the line of discovery was made by Sprengel so far back as 1790, by whom it was observed that in many plants the pollen and the seed did not come to ripeness at the same time.[BS] In some cases, the pollen is ripened before the seeds are ready; in other cases, the order of events is reversed. This observation naturally suggested transference of pollen from one plant to another; and this, connected with the continual coming and going of flies, bees, and b.u.t.terflies, led to the further discovery, that _insects_ unwittingly perform a large part of the work needful in order to _provide for fertilization_. Mr. Darwin has pointed out that from the paper of Robert Brown in the _Linnean Transactions_, in 1833; and from that of Dr. Hooker in the _Philosophic Transactions_ for 1854, the peculiar phenomena had begun to awaken scientific interest. It was, however, when the researches as to origin of species had given fresh motive to observation concerning the relations of different types of organism, that the whole facts were brought to view, separately recorded, and at length systematized so as to lead to their full interpretation. Mr. Darwin himself concentrated on the orchids as peculiarly interesting and suggestive, while a host of workers all over the world were turning their energies into this new field of observation which promised ample return for patient research.
As a reward of these investigations important facts have been established on ample evidence. First, it has been confirmed by varying lines of evidence that transference of pollen, or cross-fertilization, is of special value in the development of plant life. Investigation has strengthened the evidence of disadvantage arising from fertilization by exclusive dependence on self-produced pollen. Fritz Muller has recorded a variety of observations that the pollen of some flowers has so little influence on the seed produced on the same stem that when it falls upon the seeds no effect is produced; the pollen lies there as if possessed of no more vitalizing power than grains of dust. And, what is even more surprising, Muller has found examples in which the pollen does act upon the seeds of its own flower, but acts _injuriously_, insomuch that the flower, the pollen, and the seed-producing portion of the plant begin to decay.[BT] So deep has been the impression made on Mr. Darwin"s mind by the evidence of provision for transference of pollen, that he closes his valuable and interesting book on the _Fertilization of Orchids_ with the following statements. Having remarked that "self-fertilization would have been an incomparably safer and easier process than the transportal of pollen from flower to flower," he adds these words,--"It is hardly an exaggeration to say that Nature tells us, in the most emphatic manner, that she abhors perpetual self-fertilization."[BU]
The next result secured presents an important relation between animal life and vegetable. These flowers do not depend for their fertilization upon the action of the wind, which in scattering profusely in all directions must occasion large waste of pollen. There is found to be distinct provision for carrying the pollen from one flower to another by insects, such as the bees, whose industry in gathering honey has been celebrated from ancient times, specially because of our interest in the storehouse, but with little suspicion of the double work being done by the bees, who add to their other industry that of horticulturists. These bees are the pollen-bearers,--the recognized local carriers, regularly on the road,--doing the work which the flowers, in lack of locomotive power, could not do for each other. Or, looking at the relation of things from another point of view, the bees are at the same time gathering the honey, and sowing the seed for a future harvest. This reference to the honey, however, introduces to notice a companion series of facts, showing the provision in completed form for an interchange of services. The plants supply an attraction to the animals, while the animals render a service to the plants. This phase of interdependence is made more conspicuous by the contrast apparent in the structure and functions of plants fertilized by the wind, such as the larger shrubs and trees, which as they present a greater surface to the breeze, do not call for the same detailed provision for carrying the pollen. In contrast with these more bulky representatives of the vegetable kingdom, the more lowly and insignificant in size, as well as more short-lived, present many attractions in color, scent, and secretion of honey, all adapted to the nature of insects, suited for the work of pollen carrying. The attractions of form, color, and scent in the flowers are well known to us; but they are also appreciated by the insects,--a fact which may possibly suggest that a high degree of intellectual power is not required for appreciation of these qualities, as no one professes that bees rank high intellectually. At the same time, if comparisons are to be made at this point, the farther suggestion may also be introduced, that there is little testimony to intelligence where search for food is concerned, and while the human race do not feed on flowers, insects are constantly feeding from them. The attractions in the two cases therefore vary considerably in their significance. Restricting attention, however, to the special field of observation now before us, with the view simply of ascertaining the relations of plants and insects, color and honey present the two most prominent attractions accounting for the perpetual hum of life heard amongst the flowering plants. Different parts of the flower provide for variegated coloring, and stores of honey; these present attractions to the insects; and the structure of the flowers as they provide for the landing of the insects, and require that they penetrate to their centre for the secreted honey, secures that the work needful for fertilization be effectually done. This last feature of adaptation is that on which attention may be specially concentrated here. Mr. Darwin in treating of orchids has described this part of their structure in these words;--"In almost all the species, one of the petals (or leaves of the flower) which is properly the upper one, is larger than the others and stands on the lower side of the flower, where it offers a landing-place for insects."[BV] Towards the inner or root end of this leaf (_labellum_) is the gland, in some flowers appearing only as a slit, in others forming like a tube, (_nectary_) which secrets the honey. Just over the entrance to the part where the honey is to be found stands that which secrets the pollen prepared for fertilizing some other flower. So soon as the bee or other insect presses its head well into the centre of the flower, some of the pollen adheres to it; when the head is withdrawn, this pollen is borne off to the flower which the bee next visits; and as the head is pressed into the core of this flower the pollen is deposited, and provision for fertilization is complete.
Special features appearing in certain cla.s.ses of the orchids ill.u.s.trate how it is possible for the bee so laden to visit many flowers without depositing the pollen, yet a little later accomplish the object quite simply. The following ill.u.s.tration from Mr. Darwin"s account of the first orchid selected, will suffice. Just _above_ the entrance to the honey store, lies a pouch connected with the pollen store. As the head of the bee is pressed down towards the honey, this pouch is burst open, and from it issues a little sticky gland or disc, or it may be two of these discs. These adhere at once to the head of the bee, and being connected by a slight band with packets of pollen grains so soon as the animal retires the pollen is drawn with it, standing out like a seed vessel on the head. The strangest part of the contrivance appears in what thereafter follows. "The viscid matter has the peculiar chemical quality, of setting like cement, hard and dry in a few minutes." Suppose both the little viscid b.a.l.l.s have been withdrawn, the bands bearing the pollen will appear "projecting up like horns." "How then can the flower be fertilized? This is effected by a beautiful contrivance; though the viscid surface remains immovably affixed, the apparently insignificant and minute disc of membrane to which the caudicle adheres is endowed with a remarkable power of contraction, which causes the pollinium to sweep through an angle of about ninety degrees, always in one direction towards the apex of the proboscis, in the course of thirty seconds on an average."[BW] That is, the two erections bearing packets of pollen which formerly stood up almost perpendicular, like horns, begin to lower until they reach the horizontal; in this way when the bee enters a flower the packets of pollen inevitably touch the seed stores, communicating what is required for their fertilization. Nor have we even yet the whole of the contrivances adapted for this end. "Here comes into play another pretty adaptation." The seed vessel to be fertilized is very sticky, "but not so viscid as when touched by a pollinium to pull the whole off an insect"s head." But it is sufficiently adhesive "to break the elastic threads by which the packets of pollen grains are tied together." In this way, it tears off so much from the store adhering to the head of the bee, and still leaves there what may supply the requirements of many flowers besides. The description thus given will suffice to indicate how close is the relation of the lower orders of animal life with vegetable life, and will ill.u.s.trate how the lower organism may be dependent for existence on the higher, an ill.u.s.tration in some respect the converse of the facts ill.u.s.trating origin of species by development.
There remains in this department of inquiry only one additional set of facts, to which reference may be made, as ill.u.s.trating _distribution of work among insects and birds_, a.s.signing them to different orders of plants. This will ill.u.s.trate contrivance on a still wider scale, discovering distinct sets of affinity, which imply common localization for given plants and animals. In this it appears that flies, humble bees, and birds with long slender bills, such as the humming birds, all have a share in the work required for fertilizing plants.
There is one example, _epipactis latifolia_, with a cup-shaped labellum, in which honey is secreted, and which bees are never seen to frequent.
What, however, the bees pa.s.s, the wasps suck eagerly, and by them it is fertilized. Of this flower, Mr. Darwin says,--"It is very remarkable that the sweet nectar of this _epipactis_ should not be attractive to any kind of bee. If wasps were to become extinct in any district, so probably would the _Epipactis Latifolia_."[BX]
Another example there is of an orchid _(Spiranthes Autumnalis_), commonly known as _Ladies" Tresses_, having a series of spikes, of which the lowest flowers are first matured, the others following in order as they rise towards the summit. This plant is frequented by bees, whose practice it is to begin with the lowest flowers and ascend gradually to the top. This order in seeking to extract the honey, proves to be the proper one for fertilizing of the plant, because the pollen which the bee brings will be received by the riper flower on which it lands, and when that has been deposited, fresh pollen will adhere to the bee as it rises to the less matured flowers, and thus it departs laden with pollen destined for the lowest flowers of the next plant it visits.[BY]
[Ill.u.s.tration: 1 SECTION OF ORCHID FLOWER SHOWING POLLEN VESSEL, SEED STORE AND HONEY STORE 2 BEE ENTERING 3 POLLEN VESSEL 4 BEE RETREATING 5 BEE PREPARED FOR ENTERING ANOTHER FLOWER]
These examples introduce us to a general plan for fertilization of plants by the intervention of insects, so complete in the order of distribution that we may cla.s.sify the plants according to the insect by which they are fertilized, making it natural to speak of fly orchids, spider orchids, wasp orchids, and bee orchids. In all cases the search for honey determines the visits made, leaving still unexplained, however, the fact that the nectar of some plants is shunned by certain insects, and eagerly absorbed by others. With the general source of attraction in the flowering plants, there are diversities of arrangement among the insects, according to the comparative size of the flower, and strength required in order to penetrate to the inner chamber where the honey is stored. Because of the minuteness of the aperture, there are flowers from which the bee can not draw supplies; on the other hand, because of the size and strength of the flower, there are cases in which the ordinary bee is incapable of reaching the store, and the stronger humble bee alone succeeds in effecting an entrance.
There is thus presented in mere outline a general view of the interdependence of lower and higher orders of organism. While each flower develops pollen and seed, there are arrangements connected with the ripening of these two, which restrain or even prevent self-fertilization. Along with this there are distinct lines of evidence to establish the rule that cross-fertilization, or transference of pollen from one flower to the seed of another, secures the growth of a much healthier and more vigorous order. Where such transference is provided for otherwise than by the wind, the attractiveness of the flowers brings to them at the proper season, the insects which carry the pollen, and to each cla.s.s of insect is distributed a distinct share in the work. In these facts we have a natural law for preservation of species, discovering in a very striking manner the dependence of lower organism on higher. As Mr. Darwin has said,--" The _meaning_ of these facts is clear." Referring to the examples in which the insects have to bore holes in order to reach the honey, where there is need for time to allow for the hardening of the viscid matter, he has used the following words which are most fitly applied,--"If this double relation is accidental, it is a fortunate accident for the plants; but I can not believe it to be so, and it appears to me one of the most wonderful cases of adaptation which has ever been recorded."[BZ] It is most obviously true, as Sir John Lubbock has said, that "neither plants nor insects would be what they are, but for the influence which each has exercised on the other."[CA] In view of the facts here very briefly described it will generally be allowed that Mr. Darwin"s expectation from the study of orchids will be verified,--"An examination of their many beautiful contrivances will exalt the whole vegetable kingdom in most persons" estimation."[CB] We have enough before us to enable us to appreciate our author"s feeling when he says, "Hardly any fact has struck me so much as the endless diversities of structure,--the prodigality of resources for gaining the very same end."[CC] Again when giving us his prevailing impression he says,--"The more I study nature, the more I become impressed with ever-increasing force, that the contrivances and beautiful adaptations, slowly acquired through each part occasionally varying in a slight degree, but in many ways, with the preservation of those variations which were beneficial to the organism under complex and ever varying conditions of life, transcend in an incomparable manner the contrivances and adaptations which the most fertile imagination of man could invent."[CD]
In preparing the present summary of recent advances in this department of natural history, I have resorted freely to quotation, because of the obvious rule, that it is better for scientific interest, for proper understanding, and for regulation of all subsequent reasoning on the facts, that we have the observations presented as nearly as possible by those who made them, and that we have more general inferences in the very words of those whose minds have been filled and swayed by impressions made in the field of observation itself. In now proceeding to consider the bearing of these advances on religious thought, I shall keep as far as possible by the same rule, desiring that science may interpret itself, and translate its own special conclusions into their fit place within a scheme of the universe. And whatever there may be here of material for detailed inference, it will be taken by religious men as abundantly clear, that science in slowly unfolding to general view these secrets of nature, renders a lasting and most valuable service to religion. Our religious convictions and emotions rest on a wider intellectual basis according to the fulness with which we understand the marvels of adaptation and contrivance which lie covered from ordinary observation under the attractive surface of nature.
Altogether beyond such a general admission as this, however, it must be obvious that in the ma.s.s of deeply interesting material now before us, there lies a considerable number of truths needing to be gathered into generalized form, bearing upon the laws of nature applying to living organism. As records of details are extended before us, the marvels of structure are obvious. The multifarious contrivances become quite startling, until we are ready to lose our reckoning in the very multiplicity of facts narrated. In order to make sure of general result, we need to draw off somewhat from details,--to be content even to lose sight of many of them,--in order to gain a position, sufficiently removed for a sight of general relations. In attempting this it is clear that there are certain truths bearing on the preservation and development of species in the vegetable kingdom, and an a.n.a.logous set of truths as to the animal kingdom, and above these, possibly still more important for general appreciation of the universe as a whole, a body of truth as to the relations of plants and animals.
As to the first of these, it seems obvious that within the single field of observation presented by orchids,--comparatively narrow, in view of the wide domain of the vegetable kingdom, and yet astonishingly extensive, on account of the richness of detail,--there is a large body of evidence to support the theory of origin of species by selection and adaptation. Whether all the orchideae now found in existence have sprung from one order of plant, or from several, the testimony appears ample to support at least the following conclusion as presented in the words of Mr. Darwin, "that the now wonderfully changed structure of the flower is due to a long course of slow modification,--each modification having been preserved which was useful to the plant, during the incessant changes to which the organic and inorganic world has been exposed."[CE]
By a line of inference exactly similar, a like conclusion, must be reached as to insect life. For, important as the observations are, bearing on the transference of pollen from the place where it is generated to the place where it is wanted, we must notice that the whole work is done in consequence of search for honey by flies, moths, ants, wasps, and bees. It naturally follows that all these insects have been going through some measure of adaptation, as well as the plants. The same law must have been operating in their history while prosecuting the unceasing search for food. It may be exceedingly difficult to fill up the line of progress, or trace the causes in operation, which could favor the conclusion that all the insects named have sprung from a common stock. Still more perplexing might it be to maintain the argument that these very insects have sprung according to a sure law of descent, from vegetable life itself. But there is ample evidence to warrant the inference that in length of proboscis, formation of limbs, and other features in their structure, modifications have resulted from the struggle needful to reach the nectar secreted in the flowers.
But it is clearly impossible to stop here in our inferences. There is interdependence of lower and higher organisms, to which a distinct place needs to be a.s.signed in our theory of the universe. Even if it be granted, as it readily will be by those who have studied the results of recent research, that there is a vast body of evidence to prove that there is development of species by adaptation and selection, it is equally evident that this is not the only law affecting the existence of different orders of organized beings. Just as clear as it is that pollen and seed are both required to provide for the continuance of plant life, so clear is it that plants are needed to support insects, and insects to propagate plants. Proceeding on the same lines of reasoning as have been already employed, we must inquire how this interdependence is to be accounted for under natural law? The struggle for existence is clearly performing an important part in the development of plants, and also of animals; and so long as we regard these two orders singly, it seems obvious how changes in structure may be accounted for; but observations have become so interlaced, that a new problem has been raised in connection with facts manifestly abating the struggle for existence. In view of this problem Dr. Hooker has said,--"The adjustment of the parts of the flower to the form and habits of the insect or bird, and of these to the flower, is so accurate, that it is in vain to speculate whether the plant was adapted to feed the animal, or the animal adapted to fertilize the plant."[CF] This suggestion of the needlessness of speculation is natural from a scientific point of view, and we may do well to remember the warnings against risks attending the search for final causes, which have been sounded from the days of Spinoza to the present time; but there is a problem here which science can not leave in abeyance. The facts are undoubted, and the natural causes must be sought. The parts of the flowers are adapted to the forms and habits of the insects; the insects are adapted to the work of fertilizing the plants; the question is, How are these two things secured? The inquiry which has awakened general interest as to the development of species in the history of distinct orders such as orchids, insects, pigeons, and dogs, must strive to complete its work, by pressing on to this more complicated question concerning the adaptation of distinct organisms to influence and aid each other in the work of development. In what way science may deal with this question, and how far it may be able to advance in the search for an answer, it may be difficult to decide. For it is much easier to indicate the logical necessity for an advance, than to say in what manner the advance is to be accomplished. The one is a simple question of logical requirement; the other must be a matter of continued observation, and scientific inference. Whether science may yet discover an answer; or whether it may prove true at this point, as at other points already mentioned, that science has here reached clear marks of its own limits, must be left to the future, to be determined by those devoted to scientific research. As long, however, as this question of interdependence remains without a scientific explanation, it must be obvious that there are important facts which seem to imply some modification of the theory of descent, or evolution of species by means of selection, under the severe struggle for existence. Or, to put it from another point of view, nature has marvellously provided for mitigation of the struggle for existence, by contrivances providing both for vegetable and animal life; therefore the theory of the origin and development of life which depends chiefly on the struggle for existence must be adjusted to allow for a theory of the effects arising from the natural provision for obviating the struggle, and providing for a large increase of life.
Quite beyond this, as a matter entirely distinct, is the question as to the primordial forms of existence in the history of plants and insects.
As to this, science may be able to give very little testimony, as it is a question of the remote past, on which present facts may afford little evidence. Still, beyond these primordial forms, in a region which science can not enter, there lies the question of origin, of actual beginning, creation of life, as to the reality of which science can speak only indirectly by discovery of its own limits, in the terms of its _ultimatum_, nature has provided that such and such things shall be.
Before leaving the department of insect life, there is a collateral and complementary series of observations, bearing upon the nature and activity of ANTS, which deserves attention. The ants are a race of insects as diligently industrious as the bees, like them also fond of honey and of all sweet substances; but unlike them ready to devour other insects. Along with the industry of the bee, they have predatory tendencies, leading them into conflict with other races, or even involving different orders of their own race in warfare. It is a curious fact, in this connection, that many of the flowering plants have contrivances which guard them from the approach of ants. Creeping insects find the way barred against them while the flying insect at once and easily reaches the stores of honey, not knowing any thing of the difficulties in the path of the less favored rival. Spikes grow with their points in a downward direction, against which no creeping insect can make way; waxy or glutinous matter is spread over the leaves, which insects shun as a trap; and there are velvety flexible leaves from the edge of which the insect easily slips off. Special attention has been turned to this field of research by Kerner,[A] an interesting outline of the results of his observations being given by Sir John Lubbock.[CG]
The conclusion reached as to the utility of these contrivances for exclusion of creeping insects, is that they perform an auxiliary part in the general plan for fertilization which has been described. To allow the store of honey to go to the ants would be merely to feed them without any equivalent advantage to the flowers. To diminish the supply in this way, might cause the bees to abandon many flowers, and so greatly diminish fertilization. This would ultimately lead to short supplies, and probable extinction of several orders of plants and animals, and accordingly these contrivances to hinder the access of ants, must be added to those for facilitating the approach of bees, and other flying insects, affording further evidence of the adjustment of rival interests involved in the relations of the vegetable and animal kingdoms. The serried spikes are a phalanx of bayonets planted for resistance of an advancing foe.
Contemplating now the ants as in some respects an excluded race, which with a large share of pugnacity can not find a basis of operations for contending against the bees, we have to turn attention briefly on their modes of life. The industry of the ant is proverbial, and can not fail to arrest the attention of any one who spends a few minutes before an ant-hill. But carefully recorded observations prove it to be much greater than could have been imagined. Sir John Lubbock has rendered special service here by carefully noting the time occupied, as well as the amount of work done, thus preserving a series of observations exceedingly suggestive in many ways, and having an important bearing on a considerable number of difficult questions connected with the relative powers of lower and higher orders of life. A similar service has been rendered in America in the work of the Rev. H. C. McCook of Philadelphia, on _The Natural History of the Agricultural Ant of Texas_,--a book recording careful and most important observations, adding much to the stores of knowledge concerning ants.[CH]
The work of the ants is directed mainly to the two great objects of animal life, procuring food, and caring for the young, to which falls to be added, the repelling of attacks upon their nests, or removal of any thing obnoxious. They destroy great numbers of smaller insects, bearing them to their nests for consumption, besides going off in search of honey which may be within reach, and not guarded with spikes. This mode of providing implies a very busy life, and they do not as a rule grudge work. Besides procuring supplies, however, there is a large amount of labor in the care bestowed upon their young. Without attempting to distinguish various orders, of which "more than seven hundred kinds are known,"[CI] a general description of their young will suffice. In the earliest stage of their existence, the larvae are small conical shaped grubs, without power of movement. In this state they are fed, carried about from place to place as if their seniors were seeking change of air and temperature for them; and in process of these removals and arrangements, they are often grouped together in separate companies, and in exact order according to their size. In their next stage, they become pupae, sometimes quite exposed, in other cases covered with a thin silken covering. From this, they pa.s.s into the mature state as perfect insects, and in process of this transition older ants render a.s.sistance by way of aiding the transition, "carefully unfolding their legs and smoothing out their wings."
In the ant nest there is a singular distinction of orders which prevents us speaking of the _parent_ ants as doing all this work for the young.
The great majority in every nest are neuters, not producing young; these are the workers, and they are dest.i.tute of wings. The smaller numbers only are the males and females producing the young. The workers, shorn of wings, and entrusted with all that is required in household and out-door duties, labor a.s.siduously. These neuter ants have occasioned special perplexity to Mr. Darwin as bearing on the theory of evolution, a difficulty which is seriously increased by the fact that in some cases they "differ from each other, sometimes to an almost incredible degree, and are thus divided into two or even three castes," and these "do not commonly graduate into each other," but are "as distinct from each other as any two species."[CJ] Without following Mr. Darwin through his reasoning as to the adaptation of neuters for their task in life, it may be well to quote his words towards its close, where he says, "I must confess, that, with all my faith in natural selection, I should never have antic.i.p.ated that this principle could have been efficient in so high a degree, had not the case of these neuter insects led me to this conclusion."[CK] Besides the fact that these neuters are the workers, there is an additional circ.u.mstance, established by Mr. Frederick Smith by observations in England, confirmed by the observations of Pierre Huber in Switzerland, and afterwards verified in the clearest way by Mr.
Darwin, that there is a species of ant (_formica sanguinea_) which captures slaves of a weaker order, making war against the weaker race, carrying off their young, rearing them within their own nests, and training them to serve. Mr. Darwin was himself sceptical of such a statement, but gives an interesting narrative of distinct observations by which it was confirmed.
The amount of labor undertaken by the workers from an ants" nest, may be judged by one or two extracts from the records of Sir John Lubbock. He says, "I once watched an ant from six in the morning, and she worked without intermission till a quarter to ten at night," and in that time she had carried one hundred and eighty-seven larvae into the nest.[CL]
There is evidence not only of cooperation, but of division of labor among the workers. The observations of Mr. Forel lead to the conclusion that "very young ants devote themselves at first to the care of the larvae and pupae, and that they do not take share in the defence of the nest or other out-of-door work, until they are some days old."[CM] By a distinct set of observations, watching all ants that came and went from the nest, and laying up in captivity some of the number, Mr. Lubbock came to the conclusion "that certain ants are told off as foragers."[CN]
And in the winter season, when in the case of some orders little food is required, a few only of the inhabitants of the nest come and go, for the purpose of carrying in supplies. This makes observation much more easy at that season, rendering it possible to number and identify individual workers. The results as applicable to one of the nests are given in the following sentences. "From the 1st of November to the 5th of January, with two or three casual exceptions, the whole of the supplies were carried in by three ants, one of whom, however, did comparatively little. The other two were imprisoned, and then, but not till then, a fresh ant appeared on the scene. She carried in the food for a week, and then she being imprisoned, two others undertook the task."[CO]
One consideration more bearing upon obtaining supplies deserves to be recorded as altogether singular. Some species of ants watch over a distinct order of insects, the aphides, which exude a sweet fluid, using them exactly as we do cows for obtaining supplies of milk. The ant comes up to the aphis, gently strokes it with her feelers, forthwith the aphis gives forth its supply of honey, which the ant drinks up and departs.
The facts were observed by Pierre Huber, and verified by Mr. Darwin.
This verification was so interesting, that I give the narrative in a slightly condensed form. Mr. Darwin says,--"I removed all the ants from a group of about a dozen aphides on a dock-plant, and prevented their attendance during several hours." Mr. Darwin tried in vain by stroking the aphides with a hair, in imitation of the play of the feelers of the ants, to induce them to give up the honey. "Afterwards," he says, "I allowed an ant to visit them, and it immediately seemed, by its eager way of running about, to be well aware what a rich flock it had discovered; it then began to play with its antennae on the abdomen first of one aphis and then of another; and each, as soon as it felt the antennae, immediately lifted up its abdomen and excreted a limpid drop of sweet juice, which was eagerly devoured by the ant."[CP] So the ants have their "cows" and milk them.
To attempt any account of the ants of tropical countries, where ants are most numerous, swarming in the regions they inhabit, and marching in hosts, would occupy too much s.p.a.ce. I give, therefore, only a single reference extracted from the testimony of Mr. Savage concerning the driver ant of Western Africa (_Anomma Arcens_), so called because of the success with which it drives every thing before it. Mr. Savage annoyed by the proximity of a large settlement, discovered its quarters in some decaying granite. Kindling a fire around it, he believed he had succeeded in disposing of that settlement. Two days after, he went back to the spot, and instead of desolation and death, he found "a tree at a short distance, about eighteen inches in diameter, to the height of four feet from the ground, with the adjacent plants and earth perfectly black with them." The most striking thing, however, was that the ants had made festoons from the lower branches to the ground, formed in the following manner, as witnessed by Mr. Savage: "ant after ant coming down from above, extending their long limbs, and opening wide their jaws, gradually lengthening out the living chain" until first it was swaying to and fro, and ultimately fastened to the ground, when "others were ascending and descending upon them, thus holding free and ready communication with the lower and upper portions of this dense ma.s.s." In this same manner these ants provide for the crossing of water when on the march. "They make a line or chain of one another, gradually extending themselves by numbers across till the opposite side is reached."[CQ] This is exactly similar to the manner in which some monkeys are known to construct a natural bridge, only that the monkeys have the advantage of greater size and muscular strength, as well as prehensile power by the use of their tails. With such characteristics as have been briefly described, there is little wonder that a high place in the scale of intelligence has been claimed for these small insects. Sir John Lubbock, who has so patiently conducted his observations as to their modes of life, has stated this in the following manner,--"The anthropoid apes no doubt approach more to man in bodily structure than do any other animals; but when we consider the habits of ants, their social organization, their large communities, elaborate habitations, their roadways, their possession of domestic animals, and even in some cases of slaves, it must be admitted that they have a fair claim to rank next to man in the scale of intelligence."[CR] Whether, even with all this evidence, we may be able to rank the ants quite as high as Lubbock here suggests, may be open to question. There may, for example, be reasonable debate whether the dog does not present still higher signs of intelligence, but it says a great deal for the ants that debate in the case should be possible. A question of very great scientific importance is here raised, affecting the whole scheme of interpretation applicable to animal life, as connected with development of brain.