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tory, both scales and feathers have had a common origin in an epidermic structure, which has gradually become specialized into these organs.

While the homology between the ovum and the male cell is no reason for assuming that their functions are now alike, the constant differences between them, throughout almost all of the organic world, seem to afford a very convincing reason for believing that their functions have been specialized in two divergent directions.

If we can show that good might have resulted to the organism from such specialization, and from the restriction of certain parts of the reproductive function to one element, and the restriction of others to the other, we may feel confident that, provided variations in these directions have at any time arisen, natural selection would have seized upon and perpetuated them.

I hope to show the great usefulness of a specialization of this sort, and if I can do so, it is clear that the known differences between the ovum and the spermatozoon are reasons for a belief in its existence, while the only conclusion which can be drawn from the homology between them is, that at one time their functions were alike.

The Arguments from the Transmission of Latent Sexual Characteristics; from Reversion, and from Alternation of Generations.

In addition to the reason given by Huxley for a belief in the dual nature of each organism, he might have adduced the fact that the characteristics of each sex are potential and latent in the organism of the opposite sex, as is proved by the transmission by a father to his daughter of characteristics inherited from his grandmother.

The fact that the characteristics of one sex are latent

in the organism of the other is proved by countless wellknown illustrations, and it seems, at first sight, to afford evidence of the dual personality of each animal.

The fact in itself is so interesting that, while I believe in the possibility of a much simpler and more satisfactory explanation, it will not be out of place to devote a little space to the subject.

"In every female all the secondary male characters, and in every male all the secondary female characters, apparently exist in a latent state, ready to be evolved under certain conditions" (Darwin, Variation. Vol. ii. p. 68).

A perfect beard often begins to grow upon the face of a woman after the power of reproduction is lost by age or disease. Such women are often alluded to by Roman authors under the name of "viragines," and Hippocratus (De Morb. Vulg., Lib. vi. 55–56) has left us the description of two well-marked instances.

Aristotle (Hist. Animal, ix. cap. 36) gives an account of a hen which had ceased laying, and assumed the characteristics of the male bird, and similar change in female birds has been recorded by many writers. It has been observed in the hen, common pheasant, golden pheasant, silver pheasant, turkey, pea-hen, partridge, bustard, pelican, various ducks, cuckoo, cotinga, chaffinch, bunting, and other birds. The change may be produced by age, by disease of the ovaries, removal of the ovaries, and even (Yarrel, Phil. Trans. 1827, ii. p. 268) by removal of part of the oviduct.

Old hens which have stopped laying often acquire a comb, wattles, spurs, the brightly-colored plumage and long tail-feathers of the cock, assume the habits of the male, and even learn to crow. The bad character, as layers, of crowing hens, has even given rise to a proverb.

According to Darwin, Waterton gives a curious case of a hen which had ceased laying, and had assumed the plumage, voice, spurs and warlike disposition of the cock: when opposed to an enemy she would erect her hackels and show fight.

Female deer often acquire the horns, peculiar hair, ears, odor, and sexual desire of the males.

On the other hand, it is well known that the secondary sexual characteristics of male animals are more or less completely lost when they are subjected to castration.

Darwin states, on the authority of Yarrell, that if the operation be performed on a young cock, he never crows again; the comb, wattles and spurs do not grow to their full size, and the hackels assume an intermediate appearance between the true hackels and the feathers of the hen. Similar results are said to be produced by confinement.

Buffon states (Hist. Nat., Tom. vi. p. 80) that the horns of a stag castrated during the rutting season become permanent, but that new horns do not usually appear if it is castrated when out of heat.

Simpson says (Cyc. of Anat., Vol. ii. p. 717), "From the frequency with which castration is performed, the effect of the testes in evolving the general sexual peculiarities of the male have been more accurately ascertained than that of the ovaries upon the female constitution. These effects vary according to the age at which the removal takes place. When an animal is castrated some time before it reaches the term of puberty, the distinctive characteristics of the male are in general never developed; and the total absence of these characters, together with the softness of their tissues, the contour of their form, the tone of their voice, and their want of energy and vigor, assimilate them more in appearance and

habits to the female than to the male type. If the testicles are removed nearer the period of puberty, or at any time after that term has occurred, and when the various male sexual peculiarities have been already developed, the effect is seldom so striking: the sexual instinct of the animals, and the energy of character which these instincts impart, are certainly more or less completely destroyed, and the tone of the voice is sometimes changed to that of puberty, but the general male character of form, such as the beard in man, and the horns of ruminants, generally continue to grow."

Darwin, after reviewing these facts, concludes as follows:

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We thus see that in many, probably in all cases, the secondary sexual characters of each sex lie dormant or latent in the opposite sex, ready to be evolved under peculiar circumstances.

"We can thus understand how, for instance, it is possible for a good milking cow to transmit her good milking qualities through her male offspring to future generations, for we may confidently believe that these qualities are present, though latent, in the males of each. generation. So it is with the game-cock, who can transmit his superiority in courage and vigor through his female to his male offspring; and with man it is known that diseases necessarily confined to the male sex can be transmitted through the female to the grandson. Such cases are intelligible on the belief that characters common to the grandparent and the grandchild of the same sex are present, though latent, in the intermediate parent of the opposite sex."

Facts of this sort certainly seem, at first sight, to show the existence in each individual of two complete individualities, one from each parent; and the presence in each

sex, in a latent condition, of the organization of the other sex; but it is not difficult to show that the phenomena in question admit of a much simpler explanation.

In most cases when the sexes differ from each other in what are known as secondary sexual characteristics, that is, features which are not directly concerned in the reproductive function, the mature male is more different than the mature female from the young. I shall discuss this subject more fully in another place, so I shall give only a few illustrations at present. It will be sufficient to call attention to the resemblance between the smooth face of a woman and the face of either a boy or a girl, as contrasted with the bearded face of a man. The voice of a woman, the voice of a girl, and that of a boy, all resemble each other, and all differ from the voice of a man in the same, or nearly the same, respects.

In fowls the young of both sexes are much like the adult female in form and color.

These familiar instances are enough for our present purpose, and they show that, so far as the secondary sexual characteristics are concerned, the female is, as a rule, distinguished from the male by her failure to acquire the fully developed characteristics of the race. In these respects the female is an arrested male, and this is well shown by that fact that while the females and young of two closely related species of wild animals may be so much alike that they can hardly be distinguished, the adult males may be very different from each other.

All we need to assume, then, in order to reach a simple explanation of the secondary sexual differences between the sexes, is that each ovum has the power to develop into an organism with all the characteristics of the species, but that the female function acts, in some

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