In the adult male: Pronephros disappears. The Mullerian duct (? = pronephric duct) disappears. Mesonephros = Epididymis; its duct, the urogenital. Metanephros and duct, not clearly marked off from Mesonephros. (Compare Dog-fish, Section 19.) In the adult female: Pronephros disappears. The Mullerian duct, the oviduct. Mesonephros and Metanephros, the kidney, and their unseparated ducts, the ureters. Section 21. Hermaphrodism (i.e., cases of common sex) is occasionally found among frogs; the testis produces ova in places, and the Mullerian duct is retained and functional. The ciliated nephrostomata remain open to a late stage of development in the frog, and in many amphibia throughout life. Their connection with the renal tubuli is, however, lost. Section 22. The alimentary canal is, at first, a straight tube. Its disproportionate increase in length throws it into a spiral in the tadpole (int. Figure 11), and accounts for its coiling in the frog. The liver and other digestive glands are first formed, like the lungs, as hollow outgrowths, and their lining is therefore hypoblastic. The greatest relative length of intestine is found in the tadpole, which, being a purely vegetable feeder, must needs effect the maximum amount of preparatory change in its food. _The Development of the Fowl_ Section 23. The frog has an ovum with a moderate allowance of yolk, but the quantity is only sufficient to start the little animal a part of its way towards the adult state. The fowl, on the contrary, has an enormous ovum, gorged excessively, with yolk, and as a consequence the chick is almost perfected when it is hatched. The so-called yolk, the yellow of an egg, is the ovum proper; around that is a coating of white albumen, in a shell membrane and a shell. At either end of the yolk (Figure 1, y.) twisted strands of albuminous matter, the chalazae (ch.) keep the yolk in place. The animal pole is a small grey protoplasmic area, the germinal area (g.a.), on the yolk.