running about busily from hospital to hospital, and from lecture to lecture, in order that he might, if possible, make himself master of the expectant method, and so be prepared for the worst, he entered upon his duties at Königsberg at the close of the Easter of 1817.

Here he remained, with the exception of a few months spent at St. Petersburg, until the year 1834. It was here, therefore, that the prime of his life was spent, and the greater part of his scientific work accomplished. Happily he was never called upon to be paid for practising the expectant method on others, and he had the mingled satisfaction of looking back on his days at Vienna as for the most part wasted. In 1819 he was made Professor of Zoology and Director of the Zoological Museum; and his salary, together with other emoluments which gradually flowed in, saved him from the necessity of turning to other duties in order to earn his bread, and left him free to follow the bent of his mind. The outward life of a man devoted to science, if he have the good fortune, rare enough in this country, of being able to give himself up wholly to study, and be not cruelly dragged away from his pursuits to perform all manner of heterogeneous functions, offers but few incidents that any stranger would care to hear of. To the busy man of the world he seems to toil all day on a treadwheel, while he himself thinks he is walking in a garden of roses. Every occasion on which he comes prominently before the public, other than in his scientific capacity, be it to be rewarded with honours or to incur reproach, is to him more or less of a misfortune. He is an organ, performing a special function for the good of the body politic, and every instance of his meddling with anything else, save of course those common duties of citizenship and manhood which are as imperative on him as on any other of his fellow organs, is either a sign or the cause of disease. Admirably meagre was the outer life of Baer at Königsberg. He married and had children; he lectured and otherwise instructed his students; he laboured in the museum and in the study. He moved in the town as an able Professor and as an enlightened citizen, who was always ready to share with his fellow-townsmen the knowledge he was acquiring, and who in times of doubt and difficulty would come forward to throw into the scale of right and justice the weight of a mind made just by a daily intercourse with nature, and kept right by a steady pursuit of truth. And he fell of course into a few professorial scandals and other little quarrels, such as would naturally beset a man keenly alive to foolishness, and possessing an exceedingly caustic tongue.

His inner life was proportionately rich, and he reaped a full

harvest

harvest of scientific work. A good basketful might be made of his mere fragments, odd bits of anatomy, and stray papers published here and there, specimens of those broken pieces of fact, which every scientific worker throws out to the world, hoping that on them, some time or other, some truth may come to land. But his opus magnum, that by which he will always be remembered, on which he had already begun before he came. to Königsberg, and at which he worked almost incessantly during the whole of his stay there, is his 'History of the Development of Animals.' In this he extended human knowledge, as well by the discovery of a multitude of new facts, as by the unfolding of many great and pregnant ideas. There is a theory, not uncommon among those who talk much and know little of science, that progress, especially in what are called the sciences of observation, is effected by two classes of persons; by dull, plodding drones, who sedulously, and, as it were, blindly, through some strange kind of instinct, gather together treasures of unmeaning facts; and by rare brilliant spirits, who from time to time, without touching the facts so much as with the tips of their fingers, easily and gently arrange into laws,' and by the mere light of their genius flood with meaning, the obscure labours of their predecessors. Perhaps it need hardly be said here, that no such distinction is known in science itself. There are great men and little men, men of small and men of large ideas; every one too profits more or less by the labours of others: but if any one thing is certain it is this, that whoever wishes to build in the city of science a house that will stand, must dig his own foundations, and, to a very great extent, make his own bricks. The man who sits aloft and runs up theories out of the results of other men's toil, merely wastes his time in erecting a structure that the next stiff breeze will bring toppling down. Von Baer was an excellent brickmaker as well as a cunning builder. The numerous facts in embryology which he discovered are to be seen recorded in all the text-books of physiology, while the ideas which he was the first to set afloat concerning the nature of an animal's early growth, though for a while they failed to secure the recognition they deserved, have become part and parcel of our present biological teaching.

We spoke above of the old 'nest' theory, which taught that the offspring existed from the very beginning in the body of the parent, fully formed and perfect as to its parts, though so small as to be almost invisible. A necessary corollary further explained how the embryo itself also contained on a still smaller scale its own embryos, which in turn had still smaller embryos, and so on ad infinitum, the originator of a species actually as well as poten

tially carrying about in his body the whole family of possible descendants, one generation being 'nested' within the other. This idea, refuted by Wolff, and still further demolished by the labours of his successors, was replaced by the theory,--built on the wonderful changes seen to follow each other in the development of the embryo,—that each animal in the course of its formation runs through the long chain of all the forms that rank below it in what is called the scale of creation. Thus it was maintained that a mammal was at first an infusorium, and afterwards, even if it did not show itself as a worm, an insect, and a mollusk, it passed through the stages of a fish, a reptile, and a bird, before it achieved its final transformation. So specious and attractive a conception received, for many reasons, an enthusiastic welcome, and became a leading idea before the grounds on which it rested had been more than cursorily examined. It is Von Baer's great merit to have shown the falseness of this theory, and to have replaced it by one which has since been verified by its scientific fruitfulness, and which, at the same time, has put a new life into the science of zoology, by affording a new canon for the interpretation of the mutual affinities of living beings. The following is the briefest possible sketch of some of his chief doctrines.

Instead of an animal passing, as in a dissolving view, through all the organic forms below its own, there are certain fundamental types of formation, or ways of being formed, each one peculiar to all the members of one of the natural divisions of the animal kingdom. Thus there is a vertebrate type or way in which all vertebrate animals are formed, quite different from the molluscous type or way in which all mollusks are formed. The plan on which a bird is formed is wholly unlike the plan on which a snail is formed, and an insect is fashioned on a plan different from either. Almost the very first step in the development of an animal is the sketching out and fixing, so to speak, of the fundamental type. Thus, as we watch in a series of hen's eggs the gradual growth of the chick, the first things we see marked out are certain folds and thickenings, by which the vertebrate type is irrevocably settled. The possibility of the chick ever taking on the likeness of a mollusk, or of an insect, or of any other being than a vertebrate one, is thus in the very first scene entirely done away with. Similarly in the growth of the snail or of the bee, the first movement is the assumption of the molluscous or articulate type. In other words, in the development of an animal the most general characters are determined first.

And as the matter begins, so it goes on. To the most general characters succeed the less general, and so on, the most special

being the last to be put on. If, while an egg was being moulded into a chick, an image of it could be thrown on a screen, after the fashion of a magic lantern, so that the successive processes might be made visible to a company who understood what they saw, one might hear the following comments one after the other as the coming creature passed into being through the phases of its growth. It is a vertebrate animal! It is a vertebrate animal, that cannot live without breathing air! It is a bird! It is a land-bird! It is a fowl! It is a Dorking! As it is with birds, so is it with all animals. As it is with the whole animal, so is it with all parts, small or great. The limbs of an animal have at first only the general features of stumps or buds; afterwards they gradually put on the special characters of arms, or wings, or fins. The flesh of an animal has at first the general character of a soft granular pulp; by and bye it gains the special features of nerve, muscle, and bone. This is Von Baer's law, that in every respect and in every way the growth of a living being is a march from the general to the special-is, to use a phrase adopted by physiologists and naturalists, a process of differentiation. To this may be added as a corollary the caution to naturalists, when speaking of a being as high or low in the scale of creation, not to confound the degree of differentiation or individualisation with the character of the being's fundamental type. Thus a bee is far more highly organised, its organs and tissues are far more specialised or differentiated, than those of many fishes, and for that reason one might be inclined to give it the higher place in the scale; but the type of the bee, which is articulate, is lower than the type of the fish, which is vertebrate, and therefore the bee itself must be placed in the lower position. We may also draw the not unimportant deduction, that it is quite untrue to say, as was said during the reign of the older theory, that a man is, in one stage of his development, a fish. It would be equally true to say that a fish is, in one stage of its development, a man. All we have any right to say is, that at a particular stage the embryo of a fish cannot be distinguished from the embryo of a man. It is only by the subsequent development of special characters that we are enabled to distinguish between the fish, the reptile, the bird, and the mammal. It is only at still later stages that we can distinguish the human embryo from that of a dog or a pig.

These and other closely allied views, first promulgated by Baer, have, with various modifications and extensions, become part of the biological teaching of to-day. It has been our purpose here merely to indicate them, not to expound or to discuss them fully, nor to show what a light they have thrown on the natural affinities of animals and the distribution in time of organic Vol. 122.-No. 244.

2 A

forms,

forms, and how they have been the starting-point of many brilliant investigations. It is enough to say that they have led naturalists to regard their author with profound respect as one of the great teachers of the present day, as a worthy successor to the great Wolff, as an honourable help-meet to the illustrious Cuvier, of whose great labours they form as it were the complement, and as, in a certain sense, the forerunner of our own Darwin."

The edifice, however-the grand edifice we may call it-of biological doctrine, presented by Von Baer's 'History of the Development of Animals,' was built only at the cost of an indefatigable making of bricks. No wonder, then, we find that towards the year 1834 (the History having been published in 1828) his health began to give way. What he had already learnt urged him still forward, and seemed to promise in the future yet happier results. There floated before him visions of the discovery of grand and simple laws of organic formation. So constant was he in his work, that one year he shut himself in his house while the snow was on the ground, and did not stir a hundred steps from it until the corn was in the ear. The continual stooping position in which his short-sightedness compelled him to work ruined his digestion. His nights became sleepless. He had to read Walter Scott when he went to bed, in order to drive away visions of embryos and types, and even then the heroes and heroines often kept him awake. He felt that he was overworked and needed rest. He found it impossible now to study beyond the midday, whereas in old times he used to keep working on till late at night. He said to himself, 'The laws of natural creation will be discovered: whether by you or by some other, whether this year or in those to come, what matters it? It is mere folly in you to sacrifice for it peace and health, which none can restore to you.' Determined to break off from his labours, he looked around to see what he could do; but alas! on examining his finances, he found that all the money which had not gone in household expenses had been spent in books and in his investigations. He wanted to travel to the Adriatic and there rest awhile; but he was too poor to afford it, and too proud to ask for a subsidy from the Government. He stood for a moment face to face with that beggary which is too often the fate of those who love science too well. Just at this juncture his elder brother died childless, and his sisters begged him to come and take charge of the family estate, which would in due time come to his own eldest son, and which, though not

* Darwin and Von Baer may at least be fairly considered as mutual interpreters. We.... look at the embryo of an animal as a picture, more or less obscured, of the progenitor of all the members of the same great class.'-Darwin's Origin of Species, 4th ed., p. 533.

large,