SEX. Since the article REPRODUCTION (q.v.) includes not only some account of the reproductive processes but an outline of the comparative anatomy of the reproductive organs, and even a somewhat detailed description of the essential sexual elements, it only remains here to make a brief survey of the more important groups with respect to the absence, union, or distinction of the sexes and to the associated "secondary sexual characters" which distinctly male and female organisms so frequently and strikingly present, and to follow up that outline of the morphological facts with a brief discussion of the nature and origin of the sexes and of the theory of reproduction.
Characters of the Sexes.Starting with the Protozoa, we find indeed that union or conjugation of two or more individuals is of frequent if not universal occurrence ; yet, since, at any rate with rare and slight exceptions, no permanent morphological difference can be made out which would entitle us to speak of males or females, the group is generally defined as characterized by the absence of sexual reproduction. Without at present accepting or rejecting this view, it is convenient to postpone its discussion until the origin of sex comes to be considered.
Passing to the Ccelentcra, we find among the Hydromedusm the sexes usually distinct, and this distinction of the sexes has lately been traced back to the apparently asexual colonies from which the gonophores arise. Exceptions, however, occur,e.g., Tubularia, which is monoecious. The higher Medusas are also usually unisexual, and occasionally even show secondary sexual differences, as in the form and length of the prehensile filaments (Aurelia). Chrysaora, however, is hermaphrodite. The SipAono-phora usually present both sexes within a single colony, the gono-phores themselves being, however, unisexual. In a few cases (Apolemia uvaria, Diphyes acuminata) the colony itself is entirely male or female. The Ctenophora are invariably hermaphrodite; and among the JtJexactinia this is frequently though not generally the case, completely dioecious colonies even occurring (Gerardia). Among the Octactinia the sexes are usually distinct, even so far as the colonies are concerned, yet there are many exceptions, e.g., Corallium, which has male, female, and hermaphrodite polyps on the same stock. See HYDROZOA, CORALS, &c.
The Echinoderniata are very rarely hermaphrodite (Synapta, Ampkiura squamata), but secondary sexual characters are almost unknown. Thyone, however, has the male orifice on a small pro-tuberance. See ECHINODERMATA.
Probably no invertebrate group presents so varied and interest-ing a series of sexual phenomena as the Vermes. Thus the Polyzoa exhibit that remarkable association of hermaphroditism with asexual reproduction which so frequently recurs in organisms of vegetative habit. The Brachiopods also are hermaphrodite, as also are the Oligochajtes ; the Polychseta only exceptionally so ; some (Nereidie) exhibit secondary sexual characters so well marked as to have been mistaken for specific or even generic ones. The Plati/helminthes with few exceptions are hermaphrodite ; the Nemerteans (except Borlasia) are unisexual and occasionally exhibit secondary sexual differences. The Nematodes are very rarely hermaphrodite (Ascaris, Pelodytes), but present very marked sexual differences, the male being usually recognizable by smaller size and caudal curvature. Spicules or claspers for copulation are also present. In Strongylus the female is carried by the male in a ventral furrow. The aberrant nematoid Echinorhynchus is also dioecious. Sagitta is hermaphrodite; Balanoglossus unisexual, but without secondary sexual difference. Some of the most striking cases of sexual dimorphism are presented by the Botifera, where the male is often a fallen representative of the specific type presented by the female, having not only greatly diminished in size but having undergone thorough degeneration in structure, the alimentary canal especially becoming represented by a mere imperforate thread of cells. Nor are such cases of male degener-ation by any means confined to this group : a yet more striking instance is presented by the Gephyrean Bonellia, in which the oviduct of the large and well-grown female contains a number of almost microscopic ciliated Turbellarian-looking parasites, which have been shown to be the degenerate males. The other Gephyrea present no such extraordinary dimorphism, while the Discophora are hermaphrodite. See POLYZOA, BRACHIOPODA, ANNELIDA, NEMERTEANS, PLANARIANS, TAPEWORM, SAGITTA, LEECH, &c.
Among Crustaceans the males are frequently smaller or relatively dwarfish, sometimes attached parasitically to the female, and the sexes are generally distinguishable at least by differences in the ; structure of some of the appendages,generally, however, in evident j relation to their respective functions. Among the Copepods the sexes are separate, imd a marked tendency to dimorphism is manifested, even among the free-living forms. This is sometimes manifested in a way which suggests the sexual magnificence of the highest animals ; thus, for instance, the male Sappliirina has the brilliance of a gem. "With the appearance of parasitism in the group the reproductive relations become profoundly modified ; thus it is the always less active female which first becomes sessile and parasitic ; the male occasionally permanently retains freedom, as in the common Nicothoe of the lobster's gill; more usually, how-ever, he settles down beside or even upon the female and becomes more or less completely epi-parasitic, undergoing a more thorough degeneration than the female herself. The analogous series from free to parasitic forms furnished by the Ostraeoda and Girripcdia are yet more remarkable in their sexual degeneration, since not only does hermaphroditism become the rule, but "complementary males" (most frequently two to one female) appear. These are utterly degenerate in size and structure, in fact often quite unrecognizable as Cirripedes at all, much less as members of the same species, save for their developmental history and the existence of a few intermediate degrees of degeneration between the normal and the lost Cinipede organization, e.g., Ibla or Scalpellum, where the males of some species still retain cirri and buccal pieces. In some cases at least their male reproductive function seems to be discharged early in larval life, before the exchange of free for sessile habits, their subsequent life apparently even sinking below the level of reproductive activity. A reversal of sex has actually been alleged in some cases, the males having been said to become female. In the Phyllopods the sexes are separate, but partheno-genesis very frequently occurs, as in Daphnia, Apus, &c., and even in Apus tends to replace sexual reproduction very completely. Von Siebold examined thousands of specimens during twelve years without finding a single male; in other years, however, from 10 to 45 per cent, of males have since been found. Besides the usual copulatory modifications of appendages the males of some Phyllopods have more olfactory filaments on the antenna?. In Amphipods similar differences have been noted ; in Isopods these often become much more marked,sometimes, as in the classical case of Praniza and Anceus, reaching a degree of dimorphism with-out degeneration which is hardly exceeded in the animal kingdom, and which quite naturally led to the separation of the sexes into distinct genera. In the parasitic forms (Bopyridaj) the females degenerate much more thoroughly than the small and active males. The Schizopods exhibit considerable sexual differences. Thus among the males the antennae bear larger olfactory comb-like structures and larger abdominal members ; copulatory appendages may also be specialized ; while the females, as in many Isopods, &c, have a brood-pouch formed of overlapping ventral lamella?. The different position of the sex-openings and the characteristic forms of the limbs render the sexes easily distinguishable among the Decapods ; the crabs have an obviously broader abdomen in the female (see CRUSTACEA). Among the Arachnida, the archaic king-crabs already show slight external sex-differences; among the spiders the males have a maxillary palp specially modified for a copulatory organ, an adaptation which, associated with their often extremely small size, is of great importance in aiding their escape from their larger and ferocious mates. Some species of Theridium have a stridulating apparatus. The male scorpions on the other hand seem to possess a rather stronger development; in the Acarinas the smaller males are more distinct.lv segmented.
possess appendages modified for attachment, and sometimes retain a free habit of life as distinguished from the parasitic females. See ARACHNIDA.
Among Insects the sexes are distinguished by varying modifica-tions of different parts of the body, and differences in general form and in colour are frequent. The males are generally active and more beautiful, and seem better endowed with sense organs, though usually smaller than the females. The males have also a pre-eminence or even monopoly in producing sounds, and it is perhaps in relation to this that the psychology of sex can first be said to come within the range of observation. Thus the field-cricket is said to lower the tone of his song while caressing the female with his antenna?. In the parasitic forms dimorphism, as might be expected, becomes very marked ; in Strepsiptera the males are free and winged, while the females are blind and wingless, in fact, permanently larval. Similar cases occur in other orders, the glow-worm being probably the most familiar instance. In parasitic or abundantly nourished forms parthenogenesis very frequently appears, the extreme case being presented by Cecidomyia, a fly which exhibits rapid parthenogenetic reproduction in the larval state. The dimorphism of many beetles, in which the male frequently acquires the most extraordinary specializations of external form, has received especial attention from Darwin, whose Descent of item includes the fullest details. Here it is enough to mention that Reichenau has recently pointed out the coexistence of the larger size and relative inactivity of the male with the presence of these functionless outgrowths. The beautiful sexual dimorphism so common among the Lepidoptera need not be more than mentioned at present; while the very remarkable sexual differentiation of Hymenoptcra (bees, ants, sawflies, &c.) may also be assumed to be sufficiently familiar. See INSECTS, ANTS, BEES. In several orders (Diplera, Lepidoptera, Coleoytera) cases of dimorphism occur among the females themselves, or even among the males ; as many as three forms of females have been described in certain butterflies.
The Molluscan series opens with the normally dioecious Lamelli-branchs, of wdiich some genera (most species of Ostrea, Pecten, &c.) are, however, hermaphrodite. The Pteropods, Pulmonates, and Opisthobranchs are hermaphrodite ; the Prosobrancfis, Heteropods, and Cephalopods unisexual. Though slight differences have been described even in Lamellibranch shells (Unio), and though the internal anatomy of the essential and accessory organs is of very high complexity, the extraordinary phenomena associated with " hectocotylization " among the Cephalopod are the only marked outward manifestations of that sexual dimorphism which reaches its climax in the Argonaut. (See MOLLUSCA, CUTTLE-FISH.) The Tunicates are usually hermaphrodite; AmpMoxas, however, is unisexual (see TUNICATA).
Among Fishes hermaphroditism is extremely rare (Serranus). The males are sometimes characterized by the modification of the pelvic limbs as claspers, &c., and are at the reproductive period often readily distinguishable from the females by their brighter colour or other cutaneous changes, such as ruffling of the skin. Male and female rays are readily also distinguishable by their teeth and dermal defences. The hooked jaw of the male salmon gives him a characteristic physiognomy during the breeding season. The carp undergoes a sort of epidermic eruption at the same period ; male and female eels, too, are said often to become distinguishable both in colour and shape. Stridulating apparatus may be present, notably in the Siluroids. (See ICHTHYOLOGY.) Among Amphi-bians the bright dorsal crest of the male newt is perhaps the most striking of sex distinctions, but many male frogs and toads have vocal air sacs, epidermal callosities, and some (Cidtripes, Pelobates) possess a gland under the fore-limb. (See AMPHIBIA.)
Among the Ophidians the males are smaller, and have longer and more sleiider tails; the sexes, too, differ sometimes in colour and markings. Male Cholonians, too, have sometimes longer tails and claws and may even give voice. The submaxillary musk-gland of the crocodile is especially active in the breeding season ; the lizards have remarkable throat-pouches and crests, which may be epidermic or even correspond to cranial outgrowths, as in the chameleon.
But it is among Birds and Mammals that the observer of sexual characters finds abundant and remarkable differences extending to the minutest details, and showing how the higher evolution of parental eare which the inevitably prolonged embryonic life in-volves and the wider range of sexual selection have co-operated in modifying the whole organism. As might be expected, the lower mammals show least of this ; but as we ascend the adult males become differentiated from the females by the acquirement of gecondary sexual characters which are mainly either offensive and defensive aids for battle with each other, or which assist in gaining the admiration of the females ; and these may coexist or coincide in very various degrees. Thus scent-glands are of common occurrence from the Insectivora (perhaps even from Ornithorhynchus) upwards. Greater beauty of markings or more vivid colours are acquired,_ in m'nv Anthropidas Cbabnons, &c.) the latter being of peculiarly j crude magnificence. Abundant local growths of hair often appear, most notably in the lion and in many Anthropidx. The development of tusks and horns is also too familiar to need more than ; passing mention.
But it is unquestionable that in this as in not a few other respects the birds, rather than the mammals, have reached the highest stages of evolution. For here sexual characters no longer seem merely superadded or supplementary to the apparatus of individual life, but habits and organization alike become thor-oughly adapted to thesethe sex-differences and the reproductive j functions as it were saturating the whole life, and producing so j many and marvellous results, in habits and character, in beauty j and song, that it is not to be wondered at that the descriptive labours of the professed ornithologist have constantly risen into those of the artist and even the poet. See BIRDS, and Darwin's Descent of Man.
Nature and Determination of Sex.It is not here pro-posed to enter upon the task of historical review and criticism of the various theories of sexwhich were esti-mated at so many as five hundred at the beginning of the last century, or even to attempt any sketch of the present very conflicting state of opinion on the subject.1
Although our theories of sex may be still vague enough, the greatest step to the solution has been made in the general abandonment by scientific men of the doubtless still popular explanationin terms of a " natural tend-ency " for the production of an excess of males or the like. It is now held that " quality and quantity of food, elevation of abode, conditions of temperature, relative age of parents, their mode of life, habits, rank, etc., are all factors which have to be considered." The idea that the problem of the nature of sex is capable of being approached by empirical observation of the numbers of different sexes produced under known sets of conditions, and the obvious practical corollary of this, viz., that the proportion of the sexes must therefore be capable of being experimentally modified and regulated, are conceptions which have steadily been acquir-ing prominence, especially of late. In short, if we can find how sex is determined, we shall have gone far to investigate sex itself.
One of the most crude attempts has been that of Canestrini, who ascribes the determination of sex to the number of sperms entering the ovum, but this view has been already demolished by Fol and Pfliiger. The time of fertilization has also and apparently with greater weight been insisted upon ; thus Thury, followed by Diising, holds that the sex of the offspring depends on the period of fer-tilization : an ovum fertilized soon after liberation produces a female, while the fertilization of an older ovum produces a male. This view has been carried a step farther by Hensen, I who suggests that the same should probably hold true of the spermatozoa, and thus the fertilization of a young ovum by a fresh sperm would have a double likelihood of result-ing in a female. There are some observations which support this: thus Thury and other cattle-breeders have claimed to determine the sex of cattle on this principle, and Girou long ago alleged that female flowers, fertilized as soon as they are able to receive pollen, produced a distinct excess of female offspring.
Great weight has also been laid on the relative age of the parents. Thus Hofacker, so long ago as 1828, and Sadler a couple of years later, independently published a .body flf statistics (each of about 2000 births) in favour of ; the generalization (since known as Hofacker's and Sadler's ' law) that when the male parent is the elder the offspring are preponderatingly male : while, if the parents be of the same age, or a fortiori if the male parent be younger, female offspring appear in increasing majority. This view has been confirmed by Goehlert, Boulanger, Legoyt, and others; some breeders of horses, cattle, and pigeons have also accepted it. Other breeders, however, deny it alto-gether ; moreover, the recent statistics of Stieda and of Berner (taken independently from Alsace-Lorraine and Scandinavia) seem to stand in irreconcilable contradiction. At any rate at present we do not seem justified in ascribing greater importance to the relative age of parents than as a secondary factor, which may probably take its place among those causes influencing nourishment discussed below.
That good nourishment appears to produce a distinct preponderance of females is perhaps the single result which can at present be regarded as clearly proven and generally accepted. Yet it would be too much to say that unanimity is even here complete; thus, among plants, the experiments of Girou (1823), Haberlandt (1869), and others gave no certain result; those of Heyer (1883) have led him to dispute the validity of the generalization altogether, while Haberlandt (1877) brought evidence for regarding the excess of females as largely due to the greater mortality of the males. The investigations of agricultural observers, especially Meehan (1878), which are essentially corroborated by Dusing (1883), however, leave little doubt that abundant moisture and nourishment tend to produce females. Some of Meehan's points are extremely instruc-tive. Thus old branches of Conifers overgrown and shaded by younger ones produce only male inflorescences, a fact which may be taken in connexion with Sadebeck's obser-vation that some fern prothallia, under unfavourable con-ditions, can still form antheridia but not archegonia. The formation of female flowers on male heads of maize is ascribed by Knop to better nutrition consequent on abund-ant moisture. The only seriously contradictory observa-tions are thus those of Heyer, and it is therefore reassuring when a detailed scrutiny of his paper shows his ill-con-ducted experiments (which land him in the conclusion that the organism is not modifiable by its environment at all) to be largely capable of a reversed interpretation. The agency of temperature is also of considerable importance. Thus Meehan finds that the male plants of hazel grow more actively in heat than the female, and Ascherson states that Stratiotes aloides bears only female flowers north of 52° fat., and from 50° southwards only male ones. Other instances might be given.
Passing to the animal kingdom we find the case of insects peculiarly clear ; thus Mrs Treat showed that if caterpillars were starved before entering the chrysalis state the resultant butterflies or moths were males, while others of the same brood highly nourished came out females. Gentry too has shown for moths that innutri-tious or diseased food produced males; hence perhaps a partial explanation of the excess of male insects in autumn, although temperature is probably more important. The recent experiments of Yung on tadpoles are also very conclusive. Thus he raised the percentage of females in one brood from 56 in those unfed to 78 in those fed with beef, and in another supply from 61 to 81 per cent, by feeding with fish; while, when the especially nutritious flesh of frogs was supplied, the percentage rose from 54 to 92. Among mammals the difficulties of proof are greater, but evidence is by no means wanting. Thus an important experiment was long ago made by Girou, who divided a flock of 300 ewes into equal parts, of which the one half were extremely well fed and served by two young rams, while the other was served by two mature rams and poorly fed. The proportion of ewe lambs in the two cases was respectively 60 and 40 per cent. Dusing also states that it is usually the heavier ewes which bring forth ewe lambs.
Nor does sex in the human species appear to b independent of differences of nutrition. After a cholera epidemic or a war more boys are said to be born, and Dusing also points out that in females with small placenta and little menstruation more boys are found, and even affirms that the number of male children varies with the rise in prices. In towns and in prosperous families there are also more females, while males are more numerous in the country and among the poor. The influence of tem-perature is also marked : more males are born during the colder months, a fact noted also by Schlechter for horses.
The best known and probably still most influential theory is that systematized by Girou and known as that of " comparative vigour." This makes sex of offspring depend on that of the more vigorous parent. But to this view there are serious difficulties : thus consumptive mothers produce a great excess of daughters, not sons as might be expected from the superior health of the father. Still less weight can be attached to that form of the hypothesis which would make sex follow "genital superiority" or i " relative ardency " alone. Any new theory has thus to | reconcile the arguments in favour of each of the preceding j views, and meet the difficulties which beset all. As \ Starkweather puts it, it must at once account for such | facts as " the preponderance of male births in Europe, of | females among mulattos and other hybrid races, as also among polygamous animals, and for the equality among \ other animals. More especially it must suggest some principle of self-adjustment by which not only is the balance of the sexes nearly preserved on the whole, but by which also in cases of special disturbance the balance tends to readjust itself." Starkweather proceeds to attempt this, and his argument may be briefly summarized, j While few maintain any essential equality of the sexes, and still fewer any superiority of the female, the weight of authority has been from the earliest times in favour of the doctrine of male superiority. From the earliest ages philosophers have contended that woman is but an unde-veloped man ; Darwin's theory of sexual selection presup-poses a superiority in the male line and entailed on that sex; for Spencer the development of woman is early arrested by procreative functions : in short, Darwin's man is as it were an evolved woman, and Spencer's woman an arrested man. On such grounds we have a number of theories of sex. Hough thinks males are born when the system is at its best, more females when occupied in growth, reparation, or disease. So, too, Tiedman and others regard every embryo as originally female and remaining female if errested, while Velpau conversely regards embryos as all naturally male, but frequently degenerating to the female state. Starkweather points out some of the difficulties to the V1GW 0 f female inferiority, and lays it down as the foundation of his work that " neither sex is physically the superior, but both are essen-tially equal in a physiological sense." But, while this is true of the average, there are many grades of individual differences and deficiencies in detail, involving a greater or less degree of superiority in one or other of every pair. Starkweather's theory then is " that sex is determined by the superior parent, also that the superior parent produces the opposite sex." The arguments adduced in favour of this view, however, are scarcely worthy of it, since, save a chapter of pseudo-physiological discussion of vital forces and polarities, of superiority,nervous, electrical, etc., they rest mainly on the vague and shifting grounds of i physiognomy and temperament. And when superiority is analysed into its factors,cerebral development and activ-ity, temperament, state of health, of nutrition, etc.,soon | we find under the appearance of simplicity a law has been I obtained not by discovering any real unity under the many apparently different factors, but by simply lumping them under a common name. Nor is a rationale given of the affirmed reversal of sex, which Schlecbter and other authorities moreover wholly deny. Despite these and other faults and failures the work is interesting and often suggestive, and that not only on account of its theoretic position but its sanguine proposals for the practical control of sex.
The work of Diising (1883), while less speculative, is of great importance in respect to the causes which regulate the proportions of the sexes ; since, instead of falling back with Darwin on the unexplained operation of natural selection, he seeks to note the circumstances in which a majority of one sex is profitable, and to show that organisms have really the power to produce in such circumstances a majority of one sex,in short, that disturbances in the proportion of the sexes bring about their own compensation, and further supports these views by calcula-tion and statistical evidence.
He separates the causes determining sex into those affecting (a) one parent and (b) botli alike. Starting with a minority of one sex, he emphasizes the importance of delayed fertilization, accept-ing it as a fact that females late fertilized hear most males (this corresponding in man to a scarcity of males among the lower animals). He notes that the firstborn child is most frequently a male, especially among older persons, and thus explains how after a war, when there is a want of males, most male children are born. He ascribes importance to the amount of sexual intercourse. Thus, suppose a minority of females : their fertilization tends to occur more frequently, and thus (if the general statement be correct) they should produce a majority of their own sex ; or similarly with males. This is supported by reference to cattle-breeding, and it is interpreted physiologically to involve that young spermatozoa produce a majority of males. Suppose a great majority of males: the chances of early fertilization of the females are of course great, but eggs fertilized early tend to produce females. Or suppose conversely a great minority of males : the chances of early fertilization are small, but old eggs tend to produce males, and either excess will thus become compensated. Or again, the more decided the minority of one sex the more frequent the sexual activity of its individuals, the younger their sexual elements, and consequently the more individuals of that sex are produced. Diising next takes up as indirect causes equivalent to a minority of individuals(a) deficient nutrition ; just as frequent copulation overstrains the genital organs the same result may arise from the deficient nutrition of the system ; hence an ill-fed cow yields a female to a well-fed bull and vice versa; (b) relative age ; the nearer either parent is to the period of greatest reproduc-tive capacity the less, he thinks, is a birth of that sex probable.
As factors affecting both parents he first discusses variations in nutrition ; although means of subsistence may decrease, there is at first no decrease in the number of progeny. But it is necessary to distinguish the reproduction of the species from its multiplication, so that in defective nutrition, though an animal may not reproduce less, it will permanently multiply much less. He agrees with Darwin that the reproductive system is most sensitive to changes of nutrition; gives cases showing the effect of abundant nutrition on reproductive activity, notes the influence of climate, function, &c., and contrasts organisms of high activity, like birds and insects, with parasites. The nutritive relations of the sexes are also contrasted ; since females have to give to the embryo more than the male, they are much more dependent on food for vigour of their reproductive capacity, and hence the frequent contrast of their size, &c. Furthermore, animals suit their multiplication to their conditions of nutrition ; if food be abundant there is an increase in the number of females, and therefore a further increase in number of individuals of the species ; if food, however, be too scarce the more males are produced and the number of the species tends to diminish. Hence the connexion above mentioned between increase of children (especially females) in prosperity and after a good harvest, and the rising proportion of boys during a rise of prices. Similarly for animals: the more food the more females, and the more rapidly the species increases; the less food the more males, and the less rapid the increase. Again, plants on good soil produce more female flowers and more seed with profit to the species ; on bad soil male flowers preponderate, mostly perish, and the species tends to disappear. The extreme case of optimum nutrition tends to produce normal parthenogenesis (" thelytokie ".), yielding only females, different in cause and operation from the parthenogenesis resulting from the absence of males ("arrenotokie").
Theory of Reproduction and Sex.If we now attempt to reach a rational standpoint from which to criticize and compare the innumerable empirical conceptions of sex, much more if we seek a firm basis for the construction of a really comprehensive theory,it is evident that such a theory must be addressed not merely to the specialist concerned with problems of reproduction and development, but, while embracing details and anomalies, must be satis-factory alike to the general morphologist and physio-logist. We must therefore have before us that conception of the main lines of thought on each of these subjects which has been outlined under the headings PHYSIOLOGY and MORPHOLOGY.
The close coincidence between these two independent developments is especially to be noted. From the vague account of general form and appearance, of habits and temperaments, which made up the descriptive natural history of the past, the two streams of progress, though distinct, are wholly parallel. Thus Buffon furnished a brilliant and synthetic exposition of the oldest view, while one side of their general aspect received new precision at the hands of Linnaeus,to some extent the other also at the hands of his physiological contemporaries. The anatomical advance of Cuvier is parallel to the detailed study of the functions of the organs, while the great step made by Bichat lay in piercing below the conception of the organ and its function as ultimate, and in seeking to interpret both by reference to the component tissues. The cell-theory of Schwann and his successors analysed these tissues a step farther, while the latest and deepest analysis refers all structure ultimately to the substance called protoplasm, and similarly claims to express all function in terms of the construction and destruction, synthesis and analysis, anabolism and katabolism of this. See PHYSIOLOGY, PROTOPLASM, MORPHOLOGY.
Now, since every morphological and physiological fact or theory is in one or other of these few categories, it is evident that we have here the required criterion of theories of reproduction and sex. The question, What is sex? what is meant by male or female'? admits of a regular series of answers. The first and earliest is in terms of general aspect, temperament, and habit, and, though crude, em-pirical, and superficial, it lacks neither unity nor usefulness. At this plane are not only most popular conceptions but many theories like that of Starkweather, which may be mentioned as the most recent. The anatomist contents himself with the recognition of specific organs of sex, or at most with a similarly empirical account of their functions ; while the embryologist and histologist will not rest con-tented without seeking to refer these organs to the tissues of which they are composed and the layer from which they spring, and even reaches and describes the ultimate cellular elements essential to sex,-the ovum and spermatozoon. A parallel physiological interpretation of these is next required, and at this point appear such hypotheses as these of Weis-mann and others.
Thus the bewildering superabundance of widely dif-ferent theories at the present juncture becomes intelligible enough; and, each once classified according to its stage of progress, a detailed criticism would be easy. But this is not enough : the demand for an explanation at once rational and ultimate, to comprehend and underlie all the preceding ones, is only the more urgent. Where shall we seek for it 1 On the one hand the morphological aspect of such an explanation must interpret the forms of sex cells in terms of those of cells in general, and in terms of the structural properties of protoplasm itself ; while its more difficult yet more satisfying physiological aspect must express the mysterious difference of male and female in terms of the life processes of that protoplasm,-in terms, that is to say, of anabolism and katabolism. Were these steps made a new synthesis would be reached, and from this point it should even next be possible to retrace the progress of the science, and interpret the forms and the functions of tissues and organs, nay, even of the facts of aspect, habit, and temperament, so furnishing the deductive rationale of each hitherto merely empirical order of ob-served fact and connecting theory.
While this conception does not admit of development within the present limits, a brief abstract of such an interpretation of reproduction and of sex in terms of anabolism and katabolism may be of interest to the reader. The theory of reproduction, in general principle at least, is simple enough. A continued surplus of anabolism involves growth, and the setting in of reproduction when growth stops implies a relative katabolism. This in short is merely a more precise restatement of the familiar antithesis between nutrition and reproduction. At first this disintegration and reintegration entirely exhaust the organism and conclude its individual existence, but as we ascend the process becomes a more and more localized one. The origin of this localization of the reproductive function may best be understood if we figure to ourselves a fragment of the genealogical tree of the evolutionist in greater detail, and bear in mind that this is made up of a con-tinuous alternate series of sex-cell and organism, the organism, too, becoming less and less distinguished from its parent cell until the two practically coincide in the Protozoa, which should be defined not so much as "organisms devoid of sexual reproduction" but rather as undifferentiated reproductive colls (protosperms or protova, as they might in fact be called), which have not built up round them-selves a body. We should note, too, how the continuous immortal stream of Protozoan life (see PROTOZOA) is continued by that of ordinary reproductive cells among the higher animals, for the mor-tality of these does not affect this continuity any more than the fall of leaves does the continued life of the tree. The interpretation of sex is thus less difficult than might at first sight appear. For anabolism and katabolism cannot and do not absolutely bal-ance, as all the facts of rest and motion, nutrition and reproduc-tion, variation and disease, in short of life and death, clearly show. During life neither process can completely stop, but their algebraic sum keeps varying within the widest limits. Let us note the result, starting from the undifferentiated amoeboid cell. A surplus of anabolism over katabolism involves not only a growth in size but a reduction in kinetic and a gain in potential energy, i.e., a diminu-tion of movement. Irregularities thus tend to disappear; surface tension too may aid ; and the cell acquires a spheroidal form. The large and quiescent ovum is thus intelligible enough. Again starting from the amoeboid cell, if katabolism be in increasing preponderance the increasing liberation of kinetic energy thus implied must find its outward expression in increased activity of movement and in diminished size ; the more active cell becomes modified in form by passage through its fluid environment, and the flagellate form of the spermatozoon is thus natural enough. It is noteworthy, too, that these physiologically normal results of the rhythm of cellular life, the resting, amoeboid, and ciliate forms, are precisely those which we empirically reach on morphological grounds alone (see MORPHOLOGY, vol. xvi. p. 841).
Given, then, the conception of the cellular life rhythm as capable of thus passing into a distinctly anabolic or katabolic habit or diathesis, the explanation of the phenomena of reproduction becomes only a special field within a more general view of structure and function, nay even of variation, normal and pathological. Thus the generality, use, and nature of the process of fertilization become readily intelligible. The profound chemical difference surmised by so many authors becomes intelligible as the outcome of anabolism and katabolism respectively, and the union of their products as restoring the normal balance and rhythm of the renewed cellular life. Without discussing the details of this, farther than to note how it resumes the speculations of Rolph and others as to the origin of fertilization from mutual digestion, of the reproductive from the nutritive function, we may note how they illustrate on this view that origin of fertilization from conjugation which is the central problem of the ontogeny and phylogeny of sex. The formation of polar vesicles seems thus an extrusion of katabolic (or male) elements, and conversely its analogues in spermatogenesis (see REPRODUCTION). Passing over such tempting applications as that to the explanation of segmentation and even subsequent developmental changes, it must suffice to note that the constant insistence of embryologists upon the physiological importance of the embryonic layers bears essentially upon their respective predominance of ana-bolism and katabolism. The passage from ordinary growth to that discontinuous growth which we term asexual reproduction, and from this again to sexuality or the frequent reverse progress, is capable of rational interpretation in like manner: the " alternation of gene-rations " is but a rhythm between a relatively anabolic and katabolic preponderance; a parthenogenetic ovum is an incompletely differentiated ovum which retains a measure of katabolic (male) products, and thus does not need fertilization ; while hermaphroditism is due to the local preponderances of anabolism or katabolism in one set of reproductive cells or in one period of their life. The reversion of unisexual forms to hermaphrodite ones, or of these to asexual ones, which we have seen in such constant association with high nutrition and low expenditure,2 is no longer inexplicable. The female sex being thus prepondeiatingly anabolic, the importance of good nutrition in determining it is explained: menstruation is seen to be the means of getting rid of the anabolic surplus in absence of its foetal consumption, while the higher temperature and greater activities of the male sex express its katabolic diathesis. The phenomena of sex, then, are no isolated ones, but express the highest outcome of the whole activities of the organismthe literal blossoming of the individual life. (P. GE.)
1 As for reproduction in general, so for sex, the most convenient starting-point is the work of Hensen ('' Die Zeugung," in Hermann s lldb. d. Physiologic), while other dissertations are to be found in the leading manuals of zoology and botany, especially, however, in special papers too numerous to mention. See also REPRODUCTION, and for fuller bibliographical details see Geddes, "On the Theory of Growth, I Reproduction, Sex, and Heredity," Proc. Roy. Soc. Edin., 1886.
The above article was written by: Patrick Geddes, F.R.S.E.