In the series note the changed development of the lung rudiments, the glottis, the esophagus, the trachea, and the bronchi. The bronchi appear in pairs. Note that the liver has assumed proportions, and that it surrounds the common trunk of the vitelline veins, which it divides into two parts. The sinus venosus lies close to the heart. The ductus venosus is also surrounded by the liver. Above the tip of the ventricle we note a dilatation which represents the stomach. The hepatic, or bile duct is located immediately behind the stomach. This duct is formed by the fusion of the right and the left duct. Locate, draw, and describe the pancreas; trace the intestine; locate the splanchnic umbilicus, or yolk stalk; locate the allantois stalk, and trace its connection with the hind-gut. In the series, locate and study the Wolffian ducts, the beginning of the Müllerian duct, the embryonic kidney, or mesonephros, the permanent kidney, or metanephros. The urino-genital ridge is made up of all the above except the last named. The urino-genital ridge forms a rounded projection on each side of the mesentery into the dorsal angles of the body cavity. The Wolffian ducts empty into the cloaca. There are two ducts which may be traced far forward, and which are found to extend backward along the lateral margin of the ridge to the cloaca. Along the greater part of their length we note tubules emptying into them. Beginning near the anterior end of the urino-genital ridge, we note that the Müllerian ducts arise from a thickened line of epithelium. The greater part of the ridge is formed by the mesonephros. This is made up of a series of tubules in each of which we may distinguish two parts as follows: a tuft of capillaries from the aorta forming the glomerules, surrounded by a thin walled invaginated capsule, making up the Malpighian corpuscle; and the tubules proper. The tubules lead from the corpuscles, or glomerules, to the Wolffian duct. The germinal epithelium constitutes the essential portions of the gonad, or ovary, or testis. The germinal epithelium arises from a thickening of the peritoneum of the median wall of the ridge. The gonad is found near the anterior end of the ridge. At about this age of the embryo there should appear the primitive ovary or testis. Near the posterior termination of the Wolffian duct and from the dorsal diverticulum there arises the ureter, or metanephros duct. In these series there should be studied the heart and circulation, which will be found similar to the sections from the embryo seventy-two hours old.