tiles, and birds, and constituting the uterus and Fallopian tubes in mammals. In their earliest stage they are known as the pronephros, or "head-kidney" and answer to the permanent condition of the renal organs in worms; in their second stage they are known as the "ducts of Müller."
The second set of tubules constitute the mesonephros or Wolffian bodies; they act for a time as kidneys, and then become
Fig. 1.—Pineal Eye in Hatteria. A, nerve; B, blood-vessel; C, retina; D, greatly elongated rods and cones of retina.
the ducts of the generative organs in the male. In the female they have no later functions, but their atrophied remains persist, and give rise to various forms of cystic disease. The upper division of the Wolffian duct, with its tubes, can be found lying above the ovaries, and is known as the parovarium. It is frequently the seat of degenerative disease, not only in human beings, but in lionesses, tigresses, and cows. The middle portion often disappears, but in the cow the whole tube persists, useless always, and mischievous very frequently. Both sets of tubules, those of the pronephros and those of the mesonephros, or, in other words, the ducts of Müller and the Wolffian ducts, persist throughout life in both males and females, one set becoming
