Even nearer we come in a certain sweet-pea example, where abortion of anthers behaves as an ordinary Mendelian recessive character. By a slight exaggeration we might even speak of a hermaphrodite with barren anthers as a 'female.' Consider also how like the two kinds of differentiation are. The occasional mosaicism in Lepidoptera, called 'gynandromorphism,' may be exactly paralleled by specimens where the two halves are two colour-varieties, instead of the two sexes. Patches of Silene inflata in this neighbourhood commonly consist of hairy and glabrous individuals, a phenomenon proved in Lychnis to be dependent on Mendelian segregation. The same patch consists also of female plants and hermaphrodite plants. Is it not likely that both phenomena are similar in nature? How otherwise would the differentiation be maintained? The sweet-pea case I have spoken of is scarcely distinguishable from this. I therefore look forward with confidence to the elucidation of the real nature of sex-that redoubtable mystery. We now move among the facts with an altogether different bearing.Animals and Plants under Domestication,' from being largely a narration of inscrutable prodigies, begins to take shape as a body of coherent evidence. Of the old difficulties many disappear finally. Others are inverted. Darwin says he would have expected from the law of reversion' that nectarines being the newer form would more often produce peaches than peaches nectarines, which is the commoner occurrence. Now, on the contrary, the unique instance of the Carclew nectarine tree bearing peaches is more astonishing than all the other evidence together! Though the progress which Mendelian facts make possible is so great, it must never be forgotten that as regards new characters involving the addition of some new factor to the pre-existing stock we are almost where we were. When they have been added by mutation, we can now study their transmission; but we know not whence or why they come. Nor have we any definite light on the problem of adaptation; though here there is at least no increase of difficulties. Besides these outstanding problems, there remain many special points of difficulty which on this occasion I cannot treat-curiosities of segregation, obscure aberrations of fertilisation (occasionally met with), coupling of characters, and the very serious possibility of disturbance through gametic selection. Let us employ the space that remains in returning to the problem of variation, already spoken of above, and considering how it looks in the light of the new facts as to heredity. The problem of heredity is the problem of the manner of distribution of characters among germ-cells. So soon as this problem is truly formulated, the nature of variation at once appears. For the first time in the history of evolutionary thought, Mendel's discovery enables us to form some picture of the process which results in genetic variation. It is simply the segregation of a new kind of gamete, bearing one or more characters distinct from those of the type. We can answer one of the oldest questions in philosophy. In terms of the ancient riddle, we may : Neglecting minor complications, the descent is as follows:-Lady Penzance × Emily Henderson (long pollen) & gave purple F,. In one F, family, with rare exceptions, coloured plants with dark axils were fertile, those with light axils having sterile, whites being either fertile or sterile. The ratios indicated are 9 coloured, dk. ax., fertile : 3 coloured, lt. ax., sterile : 3 white, fertile 1 white, sterile ♂. The fertile whites, therefore, though light-axilled (as whites almost always are) presumably bear the dark-axil character, which generally cannot appear except in association with coloured flowers. This can be proved next year. Some at least of the plants with sterile are fertile on the side, and when crossed with a coloured light-axilled type will presumably give only light-axilled plants. 2 This excellent illustration was shown me by Mr. A. W. Hill and Mr. A. Wallis. A third form, glabrous, with hairy edges to the leaves, also occurs. 3 In view of Ostenfeld's discovery of parthenogenesis in Hieracium, the possibility that this phenomenon plays a part in some non-segregating cases needs careful examination. reply that the Owl's egg existed before the Owl; and if we hesitate about the Owl, we may be sure about the Bantam. The parent zygote, whose offspring display variation, is giving off new gametes, and in its gametogenesis a segregation of their new character, more or less pure, is taking place. The significance and origin of the discontinuity of variation is therefore in great measure evident. So far as pre-existing elements are concerned, it is an expression of the power of cell-division to distribute character-units among gametes. The initial purity of so many nascent mutations is thus no longer surprising, and, indeed, that such initial purity has not been more generally observed we may safely ascribe to imperfections of method. It is evident that the resemblance between the parent originating a variety and a heterozygote is close, and the cases need the utmost care in discrimination. If, for instance, we knew nothing more of the Andalusian fowl than that it throws blacks, blues, and whites, how should we decide whether the case was one of heterozygosis or of nascent mutation? The second (F2) generation from Brown Leghorn x White Leghorn contains an occasional Silver-Grey or Duckwing female. Is this a mutation induced by crossing, or is it simply due to a recombination of pre-existing characters? We cannot yet point to a criterion which will certainly separate the one from the other; but perhaps the statistical irregularity usually accompanying mutation, contrasted with the numerical symmetry of the gametes after normal heterozygosis, may give indications in simple cases-though scarcely reliable even there. These difficulties reach their maximum in the case of types which are continually giving off a second form with greater or less frequency as a concomitant of their ordinary existence. This extraordinarily interesting phenomenon, pointed out first by De Vries, and described by him under the head of Halb-' and 'Mittel-Rassen,' is too imperfectly understood for me to do more than refer to it, but in the attempt to discover what is actually taking place in variation it must play a considerable part. Just as that normal truth to type which we call heredity is in its simplest elements only an expression of that qualitative symmetry characteristic of all nondifferentiating cell divisions, so is genetic variation the expression of a qualitative asymmetry beginning in gametogenesis. Variation is a novel cell-division.1 So soon as this fact is grasped we shall hear no more of heredity and variation as opposing factors' or 'forces'-a metaphor which has too long plagued us. We cease, then, to wonder at the suddenness with which striking variations arise. Those familiar with the older literature relating to domesticated animals and plants will recall abundant instances of the great varieties appearing early in the history of a race, while the finer shades had long to be waited for. In the sweet pea the old purple, the red bicolor, and the white have existed for generations, appearing soon after the cultivation of the species; but the finer splitting which gave us the blues, pinks, &c., is a much rarer event, and for the most part only came when crossing was systematically undertaken. If any of these had been seen before by horticulturists, we can feel no doubt whatever they would have been saved. An observer contemplating a full collection of modern sweet peas, and ignorant of their history, might suppose that the extreme types had resulted from selective and more or less continuous intensification of these intermediates, exactly inverting the truth. We shall recognise among the character-groups lines of cleavage, along which they easily divide, and other finer subdivisions harder to effect. Rightly considered, the sudden appearance of a total albino or a bicolor should surprise us less than the fact that the finer shades can appear at all. At this point comes the inevitable question, What makes the character-group split? Crossing, we know, may do this; but if there be no crossing, what is the cause of variation? With this question we come sharply on the edge of human The parallel between the differentiating divisions by which the parts of the normal body are segregated from each other, and the segregating processes of gametogenesis, must be very close. Occasionally we even see the segregation of Mendelian characters among zygotic cells, knowledge. But certain it is that if causes of variation are to be found by penetration, they must be specific causes. A mad dog is not caused' by July heat, nor a moss rose by progressive culture. We await our Pasteur; founding our hope of progress on the aphorism of Virchow, that every variation from type is due to a pathological accident, the true corollary of Omnis cellula e cellula. In imperfect fashion I have now sketched the lines by which the investigation of heredity is proceeding, and some of the definite results achieved. We are asked sometimes, Is this new knowledge any use? That is a question with which we, here, have fortunately no direct concern. Our business in life is to find things out, and we do not look beyond. But as regards heredity, the answer to this question of use is so plain that we may give it without turning from the way. We may truly say, for example, that even our present knowledge of heredity, limited as it is, will be found of extraordinary use. Though only a beginning has been made, the powers of the breeder of plants and animals are vastly increased. Breeding is the greatest industry to which science has never yet been applied. This strange anomaly is over; and, so far at least as fixation or purification of types is concerned, the breeder of plants and animals may henceforth guide his operations with a great measure of certainty. There are others who look to the science of heredity with a loftier aspiration; who ask, Can any of this be used to help those who come after to be better than we are healthier, wiser, or more worthy? The answer depends on the meaning of the question. On the one hand it is certain that a competent breeder, endowed with full powers, by the aid even of our present knowledge, could in a few generations breed out several of the morbid diatheses. As we have got rid of rabies and pleuro-pneumonia so we could exterminate the simpler vices. Voltaire's cry Écraser l'infâme' might well replace Archbishop Parker's Table of Forbidden Degrees, which is all the instruction Parliament has so far provided. Similarly, a race may conceivably be bred true to some physical and intellectual characters considered good. The positive side of the problem is less hopeful, but the various species of mankind offer ample material. In this sense science already suggests the way. No one, however, proposes to take it; and so long as, in our actual laws of breeding, superstition remains the guide of nations, rising ever fresh and unhurt from the assaults of knowledge, there is nothing to hope or to fear from these sciences. But if, as is usual, the philanthropist is seeking for some external application by which to ameliorate the course of descent, knowledge of heredity cannot help him. The answer to his question is No, almost without qualification. We have no experience of any means by which transmission may be made to deviate from its course; nor from the moment of fertilisation can teaching, or hygiene, or exhortation pick out the particles of evil in that zygote, or put in one particle of good. From seeds in the same pod may come sweet peas climbing five feet high, while their own brothers lie prone upon the ground. The stick will not make the dwarf peas climb, though without it the tall can never rise. Education, sanitation, and the rest, are but the giving or withholding of opportunity. Though in the matter of heredity every other conclusion has been questioned, I rejoice that in this we are all agreed. The following Papers were read :— 1. The Coloration of Marine Crustacea. By Professor F. W. KEEBLE. 2. The Miocene Ungulates of Patagonia. By Professor W. B. SCOTT. The expeditions sent by Princeton University to Patagonia, under the leadership of the lamented Mr. Hatcher, were extraordinarily successful in collecting fossil 1 Embodied in the Report on the Colour Physiology of the Higher Crustacea (p. 299). mammals from the Santa Cruz beds, the Miocene age of which seems now to be sufficiently established. For nearly five years I have been engaged upon the Edentata of those beds, and have only recently turned to the study of the Ungulates, so that the present notice is merely preliminary. Dr. Roth, of La Plata, has lately published a very important paper, in which he shows that most of the peculiarly South American groups of hoofed animals are characterised by the structure of the periotic region, while two groups, the Litoptema and Astrapotheria, are without this character. On the other hand, all of the orders, including at least the Litoptema, have certain constant characteristics, such as the extensive articulation between the fibula and calcaneum, the convex distal end of the astragalus, which does not rest upon the cuboid, and some peculiarities in the form of the teeth. The limb and foot bones of the Astrapothina are not yet known, and their systematic position is, therefore, still a matter of conjecture. There is a striking similarity between the dentition of these animals and that of the northern genera, Cadureotherium and Metamynodon, but the form of the skull is so radically different as to make it probable that the resemblance in dentition is analogical only. It seems likely, therefore, that Roth's term, Notoungulata,' may properly be extended to include all of the Santa Cruz hoofed animals, and that all of the groups which agree in the structure of the periotic region, already alluded to, should be regarded as sub-orders of the Toxodontia. This conception is shown in the following provisional table. NOTOUNGULATA. I. TOXODONTIA. 1. Torodonta. 2. Typotheria. 3. Homalodotheria. II. LITOPTEMA. III.? ASTRAPOTHERIA. While these South American ungulates are singularly different from those of the Northern Hemisphere, it does not seem at all likely that they originated altogether independently of the latter. Ameghino has described a number of genera from pre-Patagonian formations which, though incompletely known, appear to be referable to the Condylarthra, the parent stock of the northern Ungulates. Very probably an early Eocene or late Mesozoic migration brought the Condylarthra into South America, and there, in almost complete isolation, they gradually gave rise to the various peculiar orders and sub-orders of the Notoungulata. The possibility of such migration is shown by the discovery of an armadillo in the Middle Eocene of North America. FRIDAY, AUGUST 19. The following Papers and Reports were read : 1. Heredity in Stocks. By Miss E. R. SAUNDERS. Since the rediscovery of Mendel's work experimental evidence of the purity of the germ cells has been found in a rapidly increasing number of examples. Much of this evidence is derived from cases like those studied by Mendel, where the differentiating characters are related to each other as dominant and recessive. In such cases the F, generation (DR) show the dominant character, and F, individuals the two parental characters in the ratios 3D: 1R or 1D: 1R, according as they result from DR x DR or DR × R. 2 In other cases the results may be complicated by such phenomena as reversion, TRANSACTIONS OF SECTION D. gametic coupling of distinct characters, interaction between characters in zygote (such that the second character is not manifested unless the first be also present), resolution, disintegration, &c. Such cases require minute analysis, and several generations may be needed to elucidate them. In tracing the laws of heredity in garden stocks several such complications are met with. (1) Surface character-hoary or glabrous.-Hoariness is dominant, glabrousness recessive. Simple experiments in the form DR DR or DR x R, where D is the white-flowered form of Matthiola incana, and R, a glabrous ten-week strain, give normal Mendelian ratios in F. In other cases the result as regards hoariness and glabrousness is more complex owing to the different behaviour of various glabrous strains, which, as far as can be seen, differ only in flower colour. Matings between two sap-coloured recessives, e.g., red glabrous and purple glabrous, give, as expected, glabrous offspring; but the union of the two non-sap-coloured recessives (white and cream), or of a sap-coloured and a non-sap-coloured (red or purple x white or cream) gives offspring all dominant (hoary), though both parents were glabrous. Similarly, when R, R, are recessives of different colours the unions DR, × DR, and DR, R2 give no recessives if either of the recessives used is a non-sap-coloured form. (2) Flower-colour.-Various combinations of colours give reversionary purple in F. Purple F, may also be produced by two white parents if they belong to strains differentiated by leaf-surface. Such purple cross-breds may give a simple Mendelian result in F, or a variety of new-colour forms may appear. latter result is commonly seen when cream is one of the parental colours. 2 This In the case (A), white incana x cream glabrous, F, is purple hoary. F2 shows the cross-bred and parental colours (purple, white, cream), and, in addition, three new forms, viz., red, red with cream eye, purple with cream eye. Again, in the But as the case (B), glabrous white x glabrous cream gives at least nine colour-forms in F. In both cases the glabrous recessives are all either white or cream. glabrous collectively constitute in case A one-quarter of the whole generation, and in case B presumably one-half, it is evident that the association of hoariness with colour depends on zygotic association and not on gametic coupling. Whether the Some appearance of these new forms indicates disintegration or simply recombination of The number of extracted pre-existing characters is still uncertain. Creams breed pure at once. whites are pure, others are heterozygotes with cream. recessive types resulting from a given union and their specific behaviours are not yet known. In the experiment last described we have to deal with (1) reversion in colour (2) reversion in a distinct character, leaf-surface; (3) interaction of the two characters in the zygote; (4) conceivably disintegration. The regularity with which all these phenomena occur plainly indicates that even these complex appearances result from a fundamentally simple system of Mendelian segregation. 2. On the Result of Crossing Japanese Waltzing with Albino Mice. The Japanese waltzing mice used in this experiment exhibited the well-known |