Apart from the religions and magical properties so widely accorded to the primary sexual characters, there are other reasons why they should not often have gained or long retained any great importance as objects of sexual allurement. They are unnecessary and inconvenient for this purpose. The erect attitude of man gives them here, indeed, an advantage possessed by very few animals, among whom it happens with extreme rarity that the primary sexual characters are rendered attractive to the eye of the opposite sex, though they often are to the sense of smell. The sexual regions constitute a peculiarly vulnerable spot, and remain so even in man, and the need for their protection which thus exists conflicts with the prominent display required for a sexual allurement. This end is far more effectively attained, with greater advantage and less disadvantage, by concentrating the chief ensigns of sexual attractiveness on the upper and more conspicuous parts of the body. This method is well-nigh universal among animals as well as in man. There is another reason why the sexual organs should be discarded as objects of sexual allurement, a reason which always proves finally decisive as a people advances in culture. They are not æsthetically beautiful. It is fundamentally necessary that the intromittent organ of the male and the receptive canal of the female should retain their primitive characteristics; they cannot, therefore, be greatly modified by sexual or natural selection, and the exceedingly primitive character they are thus compelled to retain, however sexually desirable and attractive they may become to the opposite sex under the influence of emotion, can rarely be regarded as beautiful from the point of view of æsthetic contemplation. Under the influence of art there is a tendency for the sexual organs to be diminished in size, and in no civilized country has the artist ever chosen to give an erect organ to his representations of ideal masculine beauty. It is mainly because the unæsthetic character of a woman's sexual region is almost imperceptible in any ordinary and normal position of the nude body that the feminine form is a more æsthetically beautiful object of contemplation than the masculine. Apart from this character we are probably bound, from a strictly æsthetic point of view, to regard the male form as more æsthetically beautiful.[139] The female form, moreover, usually overpasses very swiftly the period of the climax of its beauty, often only retaining it during a few weeks. The following communication from a correspondent well brings out the divergences of feeling in this matter: