seek to gather up a few of the discoveries of modern science which have made this region appear so wonderful.

In tracing life to its lowest forms, we find that all its essential functions may be maintained and manifested without the appearance of anything like organic structure; in fact, mere structureless · specks of jelly-like substance may be endued with that mysterious power of assimilation and motion which we term life. In 1835 Dujardin drew attention to the fact that the bodies of the lowest forms of animal life consisted of such structureless substance, to which he gave the name of Sarcode, or rudimentary flesh. Von Mohl in 1851 showed that a similar substance forms the elementary constituent of the vegetable cell, and distinguished it as Protoplasm, or primitive, organisable plastic material. And twelve years later, Professor Max Schultze proved the absolute identity of the sarcode of animals and the protoplasm of plants. This elementary substance in its typical state is described as "a semi-fluid, tenacious, glairy substance, resembling, both in appearance and composition, the albumen or uncoagulated white of an unboiled egg."

The fundamental attributes of Sarcode and Protoplasm, distinguishing them from a mere combination of chemical elements, consist in certain functions which are termed vital, and these have been already alluded to as assimilation and motion. We may analyse Protoplasm and resolve it into its component particles; but there is something which eludes chemical analysis and which distinguishes living from dead matter. Thus, dead protoplasm will readily absorb colouring matter and become stained, but no change will be visible so long as it is living, and this enables us to distinguish, in the examination of animal or vegetable tissues, between the living matter which is essential to its growth and the organised substance of which its structure is principally composed. Although we can stain dead protoplasm, we cannot compel it to perform a single act of assimilation, nor exhibit the simplest movement by its own unaided energy. Apart from and yet hidden within the mass of protoplasm there is something we cannot grasp something which defies all our skill and scientific research; something endued with such vast potentialities, that we look upon. it almost with feelings of awe and reverence, for this is the golden

link which binds all living things in one vast chain of being, and each to the Almighty Creator, to whom all nature owes its existence.

We have hitherto spoken of protoplasm in its initial condition of unorganised material, but it must be further considered in its universal relation to the higher forms of physical life, for every portion of every organism, whether animal or vegetable, has its origin in the cell, which, in its simplest form, is a minute mass of protoplasm enclosed within an integument, called the cell-wall, differing in character from the contained protoplasm, to which, however, it owes its origin, and from which it is developed by some vital action not yet very clearly ascertained. The cell-wall in plants and in some of the lower forms of animal life consists of cellulose, a substance identical in its composition with starch, turning blue under the action of iodine; differing, however, from starch in the absence of granules, its insolubility in acids and potash, and not swelling up in hot water. With reference to the production of the cell-wall, it may be asked, is there anything analogous to the enveloping skin by virtue of which small particles of liquids assume the globular form of drops, with this difference, that in the case of water and other liquids the action is purely mechanical, and no change is effected in its constitution, whereas in the enveloping tissue of the cell there is an absolute differentiation from the enclosed protoplasm, which is evidenced both in its living and dead condition?

Confining our attention to the vegetable-cell, and examining it under a sufficiently high power of the microscope, the protoplasm is seen to contain minute granules, diffused through a fluid consisting of cell-sap. This is exceedingly complex in its character, holding in solution vegetable acids, sugar, saline particles, and corpuscles of chlorophyll or colouring matter, within which are particles of oil and starch granules. The protoplasm within the cell-wall is surrounded by a layer of slightly altered protoplasmic substance, distinct from the cell-wall, but passing gradually into the inner mass of protoplasm. This inner membrane is known as the primordial or parietal utricle or ectoplasm. Embedded within the protoplasm, or in contact with the ectoplasm and the cell-wall, is usually seen during life a peculiar lens-shaped body named the

nucleus, which appears to be the centre of vital activity in the cell, and from which arise all those varied changes producing the innumerable phenomena of life. The protoplasm itself is highly absorbent of water, which, passing through the cell-wall by osmotic action, forms drops or vacuoles within the substance of the cell. So far, the operation is purely mechanical, but once brought within the sphere of vital force, chemical agency is brought into play, and the imbibed water, holding in solution gaseous, saline, and mineral particles, becomes converted into cell-sap; and through a series of marvellous metamorphoses the cell-wall, protoplasm, chlorophyll, and cell-sap each contribute in their own way to produce and store up organisable material for the further building up of its structure, and in obedience to the universal law of nature, for the propagation of its species; for the very existence of a cell-the simplest form of organic life--implies the previous existence of a similar cell, from whence is derived its origin, and to increase and multiply is but to obey an unalterable fiat.

The formation of new cells does not in every instance mean an increase in the number of cells, for there may be the renewal of a cell by the formation of the whole mass of protoplasm into a new cell; or, by conjugation, two masses of protoplasm may coalesce into a single, newly-formed cell. The multiplication of cells is more complex than either of the above processes, and this may be the result either of a part only of the protoplasm going to form the new cells or of the entire mass being converted into daughtercells. In each case the initial stage is the division of the nucleus into two parts and the formation of a cell-wall between them, with the subsequent division of each of these portions into two; consequently, the original mass of protoplasm becomes converted into four cells, each containing a nucleus. Sachs informs us that in the case of the pollen-grains of most monocotyledons, the division of the two secondary nuclei takes place in a plane at right angles to that of the division of the nucleus of the mother-cell; the four new cells consequently lie in one plane and are rounded in form. This mode of division is styled bilateral. In Dicotyledons, and in some spores, the secondary division is formed, not only at right angles to the plane of the primary division, but also

to the plane of the nucleus of the mother-cell. The daughter-cells, therefore, do not lie in one plane, but tetrahedrally, and assume a partially tetrahedral form. This form of division is called radial. In all these operations, whether simple or complex, there is, first, the assimilation, within and by the living cell, of inorganic matter and its conversion into organisable material; and secondly, the motion of a vital force acting upon this organic matter to produce those changes by which alone cell-division, multiplication, and growth can be effected.

At the Annual Meeting of the British Association at Nottingham in September last, Dr. J. S. Burdon-Sanderson, in his presidential address, referring to the science of Biology, tells us that "the term Biology was first employed after the beginning of the present century by Treviranus, who approached the subject both from the side of natural philosophy and from that of natural history. He defines life as consisting in the reaction of the organism to external influences, and contrasted the uniformity of vital reactions with the variety of their exciting causes. This definition, he adds, could still be accepted as true. It suggested the idea of organism as that to which all other biological ideas must relate. It also suggested that action was not the attribute of the organism, but of its essence; that if, on the one hand, protoplasm was the basis of life, on the other hand, life was the basis of protoplasm. Their relations to each other were reciprocal. It was the fundamental characteristic of the organism that all that went on in it was to the advantage of the whole."

Following out this thought, we shall find in the dawnings of life, both animal and vegetable, the same sequence of manifestations. Protoplasm without life as its essence is utterly inert. Life without protoplasm as its agent (if we could imagine such a condition) would be equally helpless, since the immaterial life can only act through the instrumentality of the material substance. Protoplasm under the action of life is peculiarly unstable, and the absorption of food-substances always produces more or less metabolism in its constitution, and these changes are at first in an ascending scale. The earliest operations of life, therefore, are invariably anabolic. But these constructive changes are only the starting-point of the descending scale of the katabolic operation of motion, which con

verts one cell into many, and ultimately by specialisation into the anabolism of the receptive organ, and the katabolism of the fertilising organ, in the higher phases of existence, secures continuance of life in the propagation of species. It has been stated that anabolism and katabolism are the two sides of protoplasmic life, and neither can continue independent of the other. Indeed, we may formulate this truth as a thesis, and say that living matter can only be living matter so long as these two phenomena co-exist. They act and react the one on the other in rhythmic succession, but the regularity of these alternations may be largely modified by their environment. And this fact, if borne in mind, may go far to explain some of the apparent paradoxes which confront us in the study of human biology, as well as in the investigations of the lowest forms of animal and vegetable life with which we meet in the border-land of existence.

The limits of this paper will not permit the consideration of various forms of motion other than those to which reference has been made such, for instance, as the swarming of amoeboid cells, the beautiful phenomenon of cyclosis or the rotation of fluid protoplasm within the cell, the propagation of thallotypes by the liberation of motile cells endued with vibratile cilia, and the fertilisation of phanerogams by the agency of pollen-tubes conveying the fovilla of the pollen-grain to the ovary. The investigation of these and other interesting phenomena may be left to the practical microscopist, but they are all illustrations of the fundamental principles set forth in the foregoing remarks, which, it may be observed, have been intentionally suggestive rather than exhaustive, theoretical rather than practical.

Through all the vast range of being, from the lowliest protozöon upwards to man himself, from the humblest protophyte to the noblest tree of the forest, from the merest speck of protoplasmic matter to the most highly differentiated structure of animal or vegetable tissue, one universal principle prevails, all-powerful for the maintenance and propagation of existence, and this is found in the vital action of living protoplasm; and nowhere may these phenomena be more profitably studied than amidst the wonders and beauties-wondrous and beautiful beyond poetic fancywhich may be found in the Border-land of Life.