These two great classes of conventional symbols were often represented in conjunction with each other, and thus symbolised in the highest degree the great source of life, ever originating, ever renewed. The Egyptian temple at Denderah has lately been explored by M. Mariette. In a niche of the Holy of Holies he discovered the sacred secret. This was simply a golden sistrum (see ante, pp. 44 and 70), an emblem formed by uniting the female oval O with the male sacred Tau T; and thus identical in meaning with the coarse emblem seen by Captain Burton in the African idol temple. A similar emblem is the linga standing in the centre of a yoni, the adoration of which is to this day characteristic of the leading dogma of Hindu religion. There is scarcely a temple in India which has not its lingam; and in numerous instances this symbol is the only form under which the great god Siva is worshipped. (See ante, pp. 72, 78.) The linga is generally a tall, polished, cylindrical, black stone, apparently inserted into another stone formed like an elongated saucer, though in reality the whole is sculptured out of one block of basalt. The outline of the frame, which reminds us of a Jew's harp (the conventional form of the female member), is termed argha or yoni. The former, or round perpendicular stone, the type of the virile organ, is the linga. The entire symbol, to which the name lingyoni is given, is also occasionally called lingam. This representative of the union of the sexes typifies the divine sacti, or productive energy, in union with the procreative, generative power seen throughout nature. The earth was the primitive pudendum, or yoni, which is fecundated by the solar heat, the sun, the primitive linga, to whose vivifying rays man and animals, plants and the fruits of the earth, owe their being and continued existence. These "lingas" vary in size from the tiny amulets worn about the neck, to the great monoliths of the temples. Thus the lingam is an emblem of the Creator, the fountain of all life, who is represented in Hindu mythology as uniting in Himself the two sexes. Another symbol, the caduceus, older than Greek and Roman art, in which it is associated with Esculapius and Hermes, the gods of health and fertility, has precisely the same signification as the sistrum and the lingam. This is made clear enough in the following extract from a letter by Dr. C. E. Balfour, published in Fergusson's Tree and Serpent Worship, 1878. "I have only once seen living snakes in the form of the Esculapian rod. It was at Ahmednuggar, in 1841, on a clear moonlight night. They dropped into the garden from the thatched roof of my house, and stood erect."