new daughter cells. Often, during this process, the protoplasm of the cell takes on a radiate arrangement round the poles of the spindle, producing the appearance of a sort of double star.

These appearances in the dividing nucleus were made out in various vegetable cells and in the ova of many animals; the relation between them and those described above in the quiescent nucleus seems by no means clear, but special attention has been directed to this point by Flemming 16 and by Schleicher,17 whose results in the case of the nuclei of epithelium, cartilage, &c., show a very close agreement in the main features of the process, although they differ considerably in detail. Both have directly observed the division process in living cells. Flemming has also availed himself extensively of various preservative and staining fluids, and it is in his very beautiful figures of these hardened and coloured nuclei that the chief discrepancies are observable between his results and those of Schleicher. It will be seen that their results differ in some particulars from those of former observers.

The first step, preparatory to cleavage, is a disintegration of the nuclear membrane, fragments of which seem to become mingled with the other constituents of the nucleus. Then the filaments of the intranuclear network (or the rods, filaments, and granules, according to Schleicher) assume a very lively condition of motility, and go through an extraordinary series of arrangements and re-arrangements, producing figures now star-like, now wreath-like, now more irregular, but, according to Flemming, taking place in a definite order. The filaments then assume an almost parallel disposition-forming the socalled cell-plate or equatorial plate-and then, diverging somewhat towards the equator of the nucleus, and converging at its two poles, produce the spindle form already described. The remarkable series of bacterioid movements by which these changes are produced is called by Schleicher karyokinesis:' the process is so vigorous that the nucleus of cartilage-cells, freed from its membrane, travels now to one pole of the cell, now to the other, now contracts and now enlarges to such an extent as to fill up nearly the whole cell.

After the assumption of the spindle form, the formation of the new nuclei begins, according to Schleicher, by a fusion of the converging ends of the filaments-the ends, that is, turned towards the poles of the spindle-while at the same time a separation of the fibres takes place along its equatorial plane. The young nuclei are, therefore, tolerably solid at first, but afterwards split up into filaments, rods, and granules, some of which, at the periphery of the nucleus, curve round, unite with one another, and form a new nuclear membrane. According to Flemming's observations, which are partly borne out by Schleicher's, the daughter nuclei go through the same series of

changes, but in inverse order, as were undergone by the mother nucleus in the various stages of karyokinesis.

There is one observation of Schleicher's which has an interesting bearing on Klein's view of the connection between the intra-cellular and intra-nuclear networks. He observed, in certain cases, filaments in the cell-protoplasm which seemed to become continuous with the nuclear filaments during karyokinesis. Moreover, these cell-filaments had an intimate connection with the capsule of the cell, leading to the opinion that they were split off from its internal surface by a process of delamination.

Closely connected with these researches on nuclei are the numerous observations lately made on the phenomena which accompany the maturation and impregnation of the animal ovum. The ripe egg consists essentially, in all animals, of a vitellus or protoplasmic cellbody containing usually a greater or less quantity of food material in the shape of yolk-granules, of a surrounding vitelline membrane or cell-envelope, and of an enclosed cell-nucleus or germinal vesicle, which latter is contained, like the nuclei of which we have been speaking, in a distinct membrane, and contains one or more nucleoli or germinal spots, as well as a delicate network of protoplasmic filaments.

It has long been known that, prior to impregnation, the germinal vesicle undergoes important changes, but what is the nature of these, what the precise nature of the influence exerted by the spermatozoon or spermatozoa effecting impregnation, and what the mode of origin of the nucleus of the impregnated egg or first segmentation nucleus, has only recently been made out. The observers to whom we owe this important and difficult piece of work are chiefly Auerbach, Strasburger, Van Beneden, Bütschli, Oscar Hertwig, and Fol; a résumé of their observations was published last year by Mr. Balfour,18 who has himself made important contributions to the subject. Since the publication of this résumé, the most noteworthy papers are those of Oscar Hertwig 19 and of Calberla,20 the former of whom has studied the eggs of molluscs, worms, and echinoderms, the latter those of the lamprey.

With regard to the fate of the germinal vesicle, the most complete observations are those of Hertwig, whose figures, drawn very largely from the living objects, seem to leave no doubt about the main steps of the process. The vesicle travels from the centre to the surface of the egg, its membrane undergoes disintegration, its nu

18On the Phenomena accompanying the Maturation and Impregnation of the Ovum.' Quart. Journ. of Microscopical Science, April 1878.

19 Beiträge zur Kenntniss der Bildung, Befruchtung und Theilung des thierischen Eies. Dritter Theil, I. Abschnitt.' Morphol. Jahrb., iv. Bd., 1 Heft; and 'JI. Abschnitt,' ib. 2 Heft, 1878.

20 Der Befructhungsvorgang beim Ei vón Petromyzon Planeri.' Zeits. f. wiss. Zool., xxx. Bund, 3 Heft, 1878.

cleolus disappears as such, and it is converted into a spindle-shaped body, with the usual delicate striations, and with the star-like radiation of granules from its poles. A prominence is then formed on the surface of the vitellus, into which one end of the spindle passes; the spindle itself undergoes division in the usual manner, one segment being left in the egg, the other in the prominence, which then separates itself as the first of the polar bodies' or 'directive corpuscles'—small structures now proved by their mode of formation to be true cells, which lie between the egg itself and the vitelline membrane, occupying a constant position throughout the early stages of development. The likeness between this process and those mentioned above as characteristic of ordinary cell-division will be at once apparent.

The next step is the formation, in the same manner, of a second polar body, the spindle-shaped nucleus, as before, dividing into two, one for the polar cell, the other for the egg itself. The latter portion undergoes a change, being converted into a more or less rounded body with a radial striation of granules around it, the female pronucleus (Eikern), which gradually travels to the centre of the egg. In the meantime, a (in most cases) single spermatozoon has made its way through the vitelline membrane into the vitellus, and, its tail being lost or fused with the vitellus, its head has been converted into a body closely resembling the female pronucleus, and known as the male pronucleus (Spermakern). This travels towards the female pronucleus, and completely fuses with it, the first segmentation nucleus being the result of the fusion.

As Mr. Balfour remarks, the head of a spermatozoon is, in all probability, the modified nucleus of a spermatic cell, so that the process of impregnation consists in the conjugation of two nuclei. Moreover, both ova and spermatic cells are developed in the embryo from certain cells of undetermined sex known as primitive ova,21 so that this conjugation is a union of morphologically identical structures.

21 See Balfour, 'On the Structure and Development of the Vertebrate Ovary.' Quart. Journ. of Microscopical Science, October 1878.

154

PROBABILITY AS THE GUIDE OF
CONDUCT.

THE doctrine of Bishop Butler, in the Introduction to his Analogy, with regard to probable evidence, lies at the root of his entire argument; for by the analogy which he seeks to establish between natural religion and that which is revealed, he does not pretend to supply a demonstrative proof of Christianity, but only such a kind and such an amount of presumptions in its favour as to bind human beings at the least to take its claims into their serious consideration. This, he urges, they must do, provided only they mean to act with regard to it upon those principles, which, in all other matters, are regarded as the principles of common sense. It is therefore essential to his purpose to show what are the obligations which, as inferred from the universal practice of men, probable or presumptive evidence may entail.

But indeed the subject-matter of this Introduction has yet a far wider scope. It embraces the rule of just proceeding, not only in regard to the examination of the pretensions of Christianity, but also in regard to the whole conduct of life. The former question, great as it is, has no practical existence for the vast majority, whether of the Christian world, or of the world beyond the precinct of the Christian profession. It is only relevant and material (except as an exercise of sound philosophy) to three descriptions of persons; those whom the Gospel for the first time solicits; those who have fallen away from it; and those who are in doubt concerning its foundation. Again, there are portions of these classes, to whose states of mind other modes of address may be more suitable. But every Christian, and indeed every man owning any kind of moral obligation, who may once enter upon any speculation concerning the grounds which lead men to act, or to refrain from acting, is concerned in the highest degree with the subject that Bishop Butler has opened incidentally for the sake of its relation to his own immediate purpose.

The proposition of Bishop Butler, that probability is the guide of life, is not one invented for the purposes of his argument, nor held by believers alone. Voltaire has used nearly the same words :—

Presque toute la vie humaine roule sur des probabilités. Tout ce qui n'est pas démontré aux yeux, ou reconnu pour vrai par les parties évidemment intéressées

à le nier, n'est tout au plus que probable.... L'incertitude étant presque toujours le partage de l'homme, vous vous détermineriez très-rarement, si vous attendiez une démonstration. Cependant il faut prendre un parti: et il ne faut pas le prendre au hasard. Il est donc nécessaire à notre nature faible, aveugle, toujours sujette à l'erreur, d'étudier les probabilités avec autant de soin, que nous apprenons l'arithmétique et la géométrie.

Voltaire wrote this passage in an Essay, not on religion, but on judicial inquiries: and the statement of principle which it propounds is perhaps on that account even the more valuable.

If we consider subjectively the reasons, upon which our judgments rest, and the motives of our practical intentions, it may in strictness be said that absolutely in no case have we more than probable evidence to proceed upon; since there is always room for the entrance of error in that last operation of the percipient faculties of men, by which the objective becomes subjective; an operation antecedent, of necessity, not only to action or decision upon acting, but to the stage at which the perception becomes what is sometimes called a state of consciousness.' 2

But, setting aside this consideration, and speaking only of what is objectively presented as it is in itself, a very small portion indeed of the subject-matter of practice is or can be of a demonstrative, or necessary, character. Moral action is conversant almost wholly with probable evidence. So that a right understanding of the proper modes of dealing with it is the foundation of all ethical studies. Without this, it must either be dry and barren dogmatism, or else a mass of floating quicksands. Duty may indeed be done, without having been studied in the abstract; but, if it is to be studied, it must be studied under its true laws and conditions as a science. Now, probability is the nearly universal form or condition, under which these laws are applied: and therefore a sound view of it is not indeed ethical knowledge itself, but is the organon, by means of which it is to be rightly handled. He who by his writings both teaches and inures men to the methods of handling probable or imperfect evidence, gives them exercise, and by exercise strength, in the most important of all those rules of daily life which are connected with the intellectual habits.

Different forms of error concerning probable evidence have produced in some cases moral laxity, in others scrupulosity, in others unbelief. To begin with the last named of these. It is a common form of fallacy to suppose that imperfect evidence cannot be the foundation of an obligation to religious belief, inasmuch as belief, although in its infancy it may fall short of intellectual conviction, tends towards that character in its growth and attains it when mature. Sometimes,

1 'Essai sur les probabilités en fait de Justice.'-Works (4to, Geneva 1777), vol. xxvi. p. 457.

2 Nineteenth Century, supra, pp. 606-7.