malian mother's constitution were poisoned by the production of butyric acid, that might be the cause of monstrosities in the child.

The case we have mentioned is merely an illustration, a straw that shows how the wind is blowing, but it is very suggestive. It prompts inquiry into those cases where a developing egg gives rise to many embryos (polyembryony). Is there some regularised solution of the germinal disc (blastolysis) in cases like that of the Texas armadillo which has normally quadruplet embryos, all from one ovum and all therefore of the same sex, like 'identical twins'? And what of the more extraordinary cases which are normal in certain Hymenopterous parasites where one egg gives rise to a ribbon of perhaps two hundred embryos?

Another kind of research, in which Werber has shared, concerns the influence of one developing structure on another. There is an embryological as well as a physiological correlation, as may be illustrated in the case of the Vertebrate eye. In the early embryo the eye arises as an outgrowth from the brain in the form of a club which pushes its way out till it meets the skin. There the optic club induces the formation of a lens, which is due to the embryonic epidermis, and may be pictured as the lid of what is now an optic cup. There must be a specific ferment-like influence passing from optic club to skin, and it has been shown by Werber and others that scattered lenses may arise from the breaking-up of the optic club. A fragment implanted in a quite irrelevant position will provoke the formation of a lens.

Many interesting experiments are being made on the influence of environment and diet on development. Working with tadpoles, Gudernatsch has had results which in bygone days would have given him the rank of a magician. Tadpoles fed with thyroid gland stopped growing, but continued to differentiate. Those fed with certain products of the thymus gland had their differentiation hindered rather than their growth. There are on the horizon many promising inquiries into the influence of endocrine glands on development.

One of the most interesting chapters in the new biology has to do with the experimental study of sex.

We refer to such work as that of the late Mr Geoffrey Smith, who showed that when a male crab is parasitised by a Sacculina, its whole constitution is changed. The composition of the blood-an index to the metabolismis profoundly altered. The testis disappears and its place is taken by a little ovarian tissue, which actually produces eggs. The abdominal appendages change towards the feminine type, and the male crab behaves to the Sacculina protruding under its tail as if it were a bunch of eggs! It looks as if sex were reversible, and it may be recalled that not a few animals are first male and then female in the course of their individual life. According to Mr J. T. Cunningham and Nansen the explorer, who served his scientific apprenticeship as a zoologist, the glutinous hag, a strange antiquity of a creature that lives in deep water off our coasts and sometimes bores into fishes caught on the fishermen's great lines, is one of these first-male-and-then-female animals (protandrous hermaphrodites). On a different line is that interesting but unwelcome kind of calf called a 'free-martin,' which occurs as the fellow of a male calf when there are twins of opposite sex. The 'free-martin is probably in fundamental nature a female, but it is warped in its development so that it becomes half-male. According to Prof. Lillie's ingenious theory, to which there is some opposition, the disturbing influence is due to hormones saturating through from the male brother. In any case this may serve to illustrate the fact that the study of sex is becoming increasingly experimental.

One of the most striking of recent researches is Dr Baltzer's study of a curious green worm called Bonellia, which is well known in the Mediterranean. It shows a remarkable dimorphism, for the female has a flaskshaped body an inch or two in length, with a flexible bifid proboscis much longer, while the male is very simple in structure, the merest pigmy in size, a hundred times smaller than his mate, inside whom he lives as a parasite! Baltzer found that if the newly hatched sexually indifferent larvæ of Bonellia effect attachment to the proboscis of an adult female, they develop into males; whereas, if they fail to fix themselves and sink into the sand or mud, they develop slowly (almost exclusively) into females. But the story does not end here,

for when Baltzer helped some of the very young freeswimming Bonellias to attach themselves to the proboscis of a full-grown female interesting results followed. Those that he left attached for a very short time, and then separated off, developed into almost perfect females; those that he left attached for a long time developed into perfect males, if such degenerate pigmies can be called perfect; and those that he left for intermediate periods showed practically all stages of intersex. It may be noted that several good series of intersex gradations have been studied, e.g. in Lepidoptera and in sandhoppers. There is a convergence of evidence in the direction of the conclusion that sex is an expression of deep differences in the rate and rhythm of metabolism, differences which may be swayed to this side or that by various influences. It does not seem too much to say that experimental evidence is bearing out the thesis argued for by Geddes and Thomson in The Evolution of Sex' as far back as 1889, that femaleness is associated with a relative preponderance of constructive, assimilative, or anabolic processes; and conversely for maleness.

The recent work of Prof. Oscar Riddle, which requires confirmation, goes to show that pigeons, for instance, lay two kinds of eggs, which differ in the rate or intensity of their chemical processes. One kind of egg has a relatively low storage capacity, a relatively high oxidising capacity, and a relatively greater intensity of metabolism, and such a type of egg develops into a male. The contrasted type of egg-with high storage capacity, greater energy-value in the yolk, lower metabolism, and so on-develops into a female. And it is of interest to notice that analyses of the blood of cock and hen pigeons show that the constitutional differences seen in the two kinds of egg-cells have their counterparts in the adults.

But if maleness and femaleness, fundamentally spermproducing and ovum-producing, correspond to differences in the rate and ratio of katabolic and anabolic processes, the question rises as to the cause of this difference. Two spores fall from a moss-capsule and each grows into a thread or protonema. The two threads are indistinguishable, test them as we may, but, in some cases, the one thread, or part of it, gives rise to a male moss

plant, and the other thread gives rise to a female mossplant. What is the elusive difference? Two masses of bread-mould hyphæ are identical so far as can be shown, but one must be intrinsically male and the other intrinsically female, for if two threads from the two tangles come together they form a sexual product. But if two threads from different tangles do not react when they come together, we know that these come from two 'male' tangles or from two 'female' tangles, but what the difference is we do not know.

The concept of organic evolution is accepted by all biologists as a descriptive formula that fits, but there is less contentedness with it than in the days of Darwin. The fact of the age-long advance, chequered by retrogressions, is clear; but the factors remain obscure. Throughout the millions of years there has been a succession of emergences of what must be called genuinely new 'emergents' as contrasted with 'resultants,' that is what the great process of becoming discloses, meaning by 'emergent,' as Prof. Lloyd Morgan explains, that the new organism, whether it be Insect or Mammal shows new kinds of intrinsic and extrinsic relatedness. As Prof. Lloyd Morgan says:

of any given of the stages

'Emergent evolution urges, that the "more stage, even the highest, involves the "less which were precedent to it and continue to coexist with it. It does not interpret the higher in terms of the lower only; for that would imply denial of the emergence of those new modes of natural relatedness which characterise the higher and make it what it is. Nor does it interpret the lower in terms of the higher.'

Nor does it countenance the idea of the intervention of any alien influx into 'Nature,' for that would be giving up the concept of Natural Evolution.

It must be admitted that the New Biology does not find the formula of Organic Evolution so easy as it seems to have been in bygone days. Moreover we are disappointingly ignorant of the pedigree of salient types, such as Birds or Vertebrates as a whole. We have not attained to clearness in regard to the origin of a species; we are not even sure what a species means!

The central problem in evolution is the origin of the

new-a mathematical genius, an intelligent dwarf, a ten-foot tailed cock, a copper-beech, a greater celandine with laciniate leaves, an entirely novel evening primrose. We distinguish these as variations or mutations from exogenous modifications directly impressed on the individual body by peculiarities in environment, food, and function. It remains uncertain that these modifications can be transmitted as such or in any representative degree; but the transmissibility of many kinds of variations is incontrovertible. So it is to variations mainly that we look as furnishing the raw material of evolution. We know also more clearly than in Darwin's day that variations are due to permutations and combinations In within the germinal material. many cases it is possible to go further and say that novelties are due to shufflings and reshufflings of those hereditary cards which lie in the nuclear rods (or chromosomes) of the germ-cells, or, in some cases, to changes in the cards themselves. The germinal representatives of many at least of the hereditary characters lie in definite linear order in the chromosomes, and it is possible to say, for instance, that the hereditary factor' or 'gene' for or contributing to a particular adult character lies in the lower third of the fourth chromosome of the germ-cell. In the fruit-fly Drosophila there are known to be about 7500 of these 'factors,' 'determiners,' or 'genes'; and it is plain that their shuffling must allow of many diverse hands' of cards. Opportunities for new arrangements are afforded by the intricate nuclear changes which occur in connexion with the maturation and fertilisation of the germ-cells. It may also be that environmental, nutritional and habitudinal peculiarities, deeply saturating through the body, pull the trigger of germinal changefulness. Or it may be that there are more spontaneous reorganisations of the implicit organisms we call germ-cells, and that a 'gene' itself may change. It is clear that the new biology will have its hands full in prosecuting the study of variation.

In two books recently published on evolution we find two extraordinarily divergent statements in regard to heredity. In one, Prof. Lotsy says: 'Of heredity we know nothing.' In the other, Prof. T. H. Morgan says: The problem of heredity may be said to be