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 glosso-pharyngeal 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 museum specimens each of which represents the development of a day up to and including the twenty-first day. THE DERIVATIVES OF THE GERM-LAYERS From the three primary germ-layers are developed the various tissues and organs of the body by metamorphoses which may be referred to the two fundamental processes of specialization, or the adaptation of structure to function, and of unequal growth, which latter results in the formation of folds, ridges, and constrictions. From the ectoderm are produced: The epidermis and its appendages, including the nails, the epithelium in connection to the feathers and the feathers. The infoldings of the epidermis, including the epithelium of the mouth, epithelium of the salivary glands and the anterior lobe of the pituitary body, or hypophysis. The epithelium of the nasal tract with its glands and communicating cavities. The epithelium lining the external auditory canal, including the outer stratum of the membrana tympani. The lining of the anus. The epithelium of the conjunctiva and of the anterior part of the cornea, the crystalline lens. The spinal cord, the brain with its outgrowths, including the optic nerve, the retina, and the posterior lobe of the pituitary body. The epithelium of the inner ear. From the entoderm are produced: The epithelium of the respiratory tract. The epithelium of the digestive tract, from the back part of the pharynx to the anus, including its associated glands, the liver, and the pancreas. The epithelial parts of the middle ear and of the eustachian tube. The epithelium of the thymus and the thyroid bodies. From the mesoderm are developed: Connective tissue in all its modified forms, such as bone, cartilage, lymph, blood, fibrous and areolar tissue. Muscle tissue. All endothelial cells, as of joint-cavities, bursal sacs, lymph sacs, blood-vessels, pericardium, and endocardium, pleura, and peritoneum. The spleen. The kidneys and ureters. The testicles and the system of excretory ducts. The ovary and oviduct. PREPARATION OF STRUCTURES FOR STUDY It is hoped that the following suggestions will be helpful in the laboratory work.