OUTLINE FOR LABORATORY STXJDY OF THE CHICK 341 



tine; locate the splanchnic umbilicus, or yolk stalk; locate the allan- 

 tois stalk, and trace its connection with the hind-gut> 



In the series, locate and study the Woffian ducts, the beginning 

 of the Miillerian 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; ^-'.ii 



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 tubulies emptying into them. 



Beginning near the anterior end of the urinogenital ridge, we note 

 that the Miillerian 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, mak- 

 ing 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. 



Work out a summary of the relations of the allantois and the 

 yolk stalk to the intestines; the relations of the Wolffian ducts to the 

 intestines; the origin of the ureters from the Wolffian ducts; the 

 relations of the lungs, the liver, and the thyroid gland; the relations 

 of the blood-vessels; a study of the muscle plates; the relations of 

 epiphysis, hypophysis, infundibulum, mouth, and pharynx; the 

 relations of the vagus, or pneumogastric, trifacial, acoustico-facialis, 

 and glossopharyngeal nerves to the visceral arches. 



In addition to the study of embryos at the end of each of the 

 first four days of incubation, a study should be made of preserved 



