WOLFF'IAN BODIES, important organs in the vertebrate embryo, in which they serve only a temporary purpose, except in the lowest class (the fishes), where they remain permanently. In the development of the chick, these bodies may be seen as early as the fourth day, lying along either side of the vertebral canal, from the region of the heart downward and backward, and consisting of a series of meal or blind appendages, corresponding with the so-called kidneys of fishes, which in reality are trite persistent Wolitian bodies. On the fifth day, the appendages become convoluted, and the body which they collectively form increases in mass. The appendages are then seen to pos sess a secreting property, and the fluid which they secrete is conveyed by the duct of each side into the allantois, a sac winch, at the same time, acts as a temporary respira tory organ, and is also used as a urinary bladder. Hence these organs may be regarded in the light of temporary kidneys. In the chick, the true kidneys begin to form from the Wolitian bodies at the fifth or sixth day, and gradually increase in size as the tempor ary organs diminish; and at the end of fetal life, only a shrunken rudiment of them can be observed. In man, the process is very similar, the Woffilan bodies beginning to
appear toward the end of the first month; while in the seventh week, the true kidneys; first present themselves. From the beginning of the third month, the Wolflian bodies: begin to decrease, the kidneys increasing in a corresponding ratio, and at the time birth, scarcely any traces of the former can be seen. It was formerly believed that the essential parts of the generative apparatus—the testes in the male and the ovaria in the. female—were also developed from these bodies; but this is not the case, as they have an, independent origin in a special mass of blastema peculiar to themselves,in the immediate vicinity of the Wolflian bodies.—See Carpenter's Principles of Iluman Physiology.