specialized from the general vertebrate type, just as the vertebræ themselves have risen from their first rude outlines to their present and modified condition.

Thus have grown the ideas which the casual study of a broken sheep's skull first generated; and thus do we find an illustration of the method in which a study of homology leads us towards an understanding of the true nature of an organ or part in living beings. But for this science of likeness-but for the results of long, careful, and laborious research into the comparisons which may be legitimately drawn between the formation of the skull in one animal and in another-the answer to the question "What is a skull?" might have been left in the position of a riddle propounded by the Sphinx itself. Thus much has resulted from the study of likenesses— namely, a clear gain of much knowledge concerning the true nature of an intricate portion of the animal frame. It yet remains to be shown how the progress of evolution has helped and aided the true understanding of the modifications which the skull has undergone in its progress from the unspecialized type of primitive vertebrate life; and, conversely, how the existence of such modifications aids, confirms, and supports the basis on which the development theory may be said to rest. Says Professor Parker, "We are necessarily led to see that this unity of structure, this relationship, includes extinct creatures as well as those now living. And the student cannot but seek for some further light than is involved in the establishment of the fact that there is a unity in the structure of all vertebrate skeletons. An explanation is required; we want to comprehend how this unity in diversity has come about. Morphology (the science of structure), studied in the history of embryos, reveals to us an evolution by which the skull passes through one grade of structure after another, becoming advanced and changed by almost imperceptible gradations until the adult type is attained, in a certain number of days and weeks. This evolution is continually going on within our experience, and we little think of its marvels. And yet many find it inconceivable that the same process of evolution can have taken place in past ages, so as to produce from small beginnings the varied fauna of the globe. "The natural forces which in a few days," concludes Mr. Parker, "make a chick out of a little protoplasm and a few teaspoonfuls of yolk, are pronounced incompetent to give rise to a slowly changing, gradually developing series of creatures, under changed conditions of life. Yet to our minds the one is as great a marvel as the other; in fact, both are but the different phases of one history of organic creation,"

Thus the old idea of the “archetype" is seen to become resolved into, and to be replaced in time and through the progress of scientific research by, the primitive form from which all the varied structures of the same kind have arisen by a natural process of evolut The science of likeness and the theory of development mutuz support and confirm each other. No longer do we search for "archetype" skull or for a typical vertebra. The creative idea this or in any other department of natural science is not contained in some perfectly formed structure, with all its complexities and intricacies of form already apparent. The true object of our search is for the primitive type; and the way of our seeking lies through the modifications and paths by which, from that simple type, the abstruse and the complex have been evolved.

The present is perhaps the most appropriate stage of our inquiries at which to point out that, whilst the broad features of likeness in a series of animals or plants—such as those exemplified by the limbs of higher animals-are only susceptible of explanation on the theory of evolution, or, in other words, "of inheritance from a common ancestor," there are other features which demand a somewhat different method of treatment. When the subject of homologies is regarded in a broader aspect, we become aware that it is not only possible, but necessary, to regard likenesses from two points of view. The broad homologies of limbs are to be explained, as just remarked, by the theory of descent from a common ancestor. Such structures, the direct product of blood-relationship, are to be called "homogenous," and illustrate the purest examples of the "likenesses" we are discussing. But it has been already remarked that a law of "adaptation" forms, along with descent, a factor of no slight importance in modifying the structures of living beings. Every living thing is subject to the perpetual and continuous action of its environments or surroundings. Such outward influences may favour or retard the evolution and growth of new parts and organs, and will unquestionably induce now, as in the past, alterations in the structure and form of the living being. Of the exact influence and extent of the external causes of variation we know very little, but of the existence of such causes no one entertains a doubt. The question, however, presents itself as to the nature of the likenesses and differences which such outside influences may produce. All likenesses or homologies which cannot be accounted for on the theory of descent from a common ancestor are named "homoplastic," according to Mr. Ray Lankester's terminology. As an example of both kinds of likeness, it may suffice to cite the limbs and heart of higher verte

brata and the swimming-bladder of fishes, as illustrative of "homogenous" parts, or those which are the products of inheritance. The heart of a bird and a quadruped are "homogenous" organs, but the cavities or compartments are "homoplastic," or, in other words, have been developed independently of each other, as, in all probability, have the feathers of the one and the hairs of the other. It is well, therefore, to take into account this false or incomplete "likeness," which expresses no blood-relationship, and which, in its production, involves much that is obscure. We can explain the likeness between limbs on the theory of descent from a common type; the likeness between a worm and a lobster, in respect of their jointed bodies, becomes clear on this theory; but we cannot so account for the close likeness between the individual joints of a worm, or between those of a lobster, or, for that, between the feelers, jaws, and feet of the latter animal, on the principle of inheritance. Mr. Darwin says: "The formation of such structures may be attributed in part to distinct organisms, or to distinct parts of the same organism, having varied in an analogous manner, and in part to similar modifications having been preserved for the same general purpose or function."

Leaving, as still under the shadow of unapprehended causes, the variation of parts from outward forces operating upon the living being and its structure, let us turn to some clear examples of plain, though at first sight unapparent, "likenesses," which may be drawn from both animal and plant kingdoms. Our examples may comprise a wide range of subjects; but this facility of illustration is in itself a proof of the universal application of the science of likeness to - explain the modifications of common types through which the forms of life have come to exhibit that diversity which is at once the wonder and the charm of living nature.

No better starting-point can well be found than within the region of flowers and fruits, whereof many familiar objects may be shown to teem with the lessons of highest philosophy. Once again,

Goethe's name comes to the front as the chief originator and expounder of those likenesses between very diverse organs, the true import of which relationship the great poet-philosopher himsel did not fully comprehend. In his work "Versuch die Metamor phosen der Pflanzen zu erklären," bearing date 1790, Goethe following hard upon Caspar Friedrich Wolff, enunciated his thoughts concerning the "Metamorphoses" of plants. It is necessary first all to clearly understand the significance of this phrase "metamorphosis," and its applications to the study of likenesses. With Goethe VOL. CCXLVII. NO. 1798.

F F

the phrase implied what we now term "abnormal development." It meant the chronicle of the changes which might take place in the usual plan or type in which a plant was built up. The production of a "double flower" was to Goethe, as it is to us to-day, an example of metamorphosis of the alteration of parts from their normal type. What may be said, however, to be the bearing of these discoveries on the elucidations of the problems of animal and plant forms and existence? The reply is clear to us to-day, although to the believer in "freaks of Nature" the question would have been impossible of solution. To the latter, a monstrous development, or a departure from the ordinary type of things, was an evidence that Nature was given occasionally to play strange pranks without reason or meaning. The very phrase "sports" of Nature, applied to the monstrosities or abnormalities thus produced, indicates with sufficient clearness the opinion respecting the frivolity of Madre Natura which the old naturalists entertained. A double flower and a "Two-Headed Nightingale" were equally good illustrations of the "freaks" in which Nature was wont to indulge. The idea that possibly the production of a monstrosity in animals and plants was as directly due to the operation of law as the birth of natural progeny was never entertained, until the genius of Goethe and his successors pointed out that in the so-called abnormalities of life we might find a clue to the primitive forms of living things. In the production of her "freaks" Nature was "showing her hand," so to speak, and lifting a corner of the veil in which her ways of developinent were so thickly enshrouded. The transformations and metamorphoses of animals and plants, viewed in this light, are but the occasional return of Nature to primitive ways and methods of working. On the idea that living things have not always existed as they now appear, we behold in deviations from the normal type a clue to the stages and states of long ago. On the theory that creation has been from the first a stable and unaltering collection of living forms, the metamorphoses and variations of animals and plants are simply grounds for wonderment and vain surprise.

Amongst the most important of the generalisations which Goethe deduced from his study of the variations of plant structure and life, was that which held that "the leaf is the type of the whole plant." Not merely can it be shown that every appendage of the stem is a leaf of one kind or another, but it may also be proved that the plant itself arises from a seed which is in its essential nature merely a peculiarly modified bud. Strange indeed is it to think that between the gorgeous beauty of the blossom, or the complex nature

of the flower and its parts, and the simple leaf, there should exist such close and intimate connection. But the likenesses or homologies which underlie the varied forms of plants may be readily illustrated by a brief reference to familiar facts of flower structure. Flower buds spring from the protective base of leaves called bracts. Now, these leaves exhibit every transition and gradation, from the ordinary leaf of the plant to the more characteristic leaf we see protecting the flower bud. Next in order, the botanist asks us to note that bracts themselves may insensibly pass by easy ways and gradual stages to correspond with the outer parts of the flower. There are four parts in a

perfect flower (Fig. 1), arranged as circles or whorls of leaves placed in an alternating fashion as to the individual leaves, one whorl within the other. Beginning at the outside of the flower, we find the calyx (ca), composed, as a rule, of green leaves called sepals. Next comes the brightly coloured part-without which, in popular acceptation, a "flower" would not merit the name-the corolla (co), composed of leaves called petals, which alternate with the sepals. These two outer whorls are the floral envelopes. Within the corolla, we find the stamens (st), each consisting of a stalk and a head, in which latter is developed the yellow dust called pollen, by which the ovules are fertilised and converted into the fertile "seeds." Last of all, and in the centre of the flower, the pistil (p) is to be noted. This part consists of one or more carpels, in each of which we note a lower part called the ovary, wherein the ovules (which become the seeds after fertilisation with the pollen) are contained. Thus much by way of a brief lesson in elementary botany. Now, when we study the bracts, we find that insensibly these have a tendency in many flowers to become like the green sepals of the calyx. Look at a Camellia in bud. You will see the numerous bracts, and also the five sepals, and you will further gain a good idea from this familiar example of the absolute identity which may exist between bracts