4 LABORATORY OUTLINES FOR EMBRYOLOGY 



THE EGG 



An egg is a cell and has all the essential parts of a cell. 

 However, in the egg, some of the parts have special 

 names. The cell-wall is called the vitelline membrane; 

 the nucleus is called the germinal vesicle; and the nucle- 

 olus is called the germinal spot. An egg differs further 

 from most other cells in that it contains yolk material. 

 This yolk material is called deutoplasm. 



-i. Formation of an Egg 



Eggs are produced by special glands called ovaries. 

 The ovary is covered by a layer of cubical cells called 

 the germinal epithelium. The eggs are formed from this 

 germinal epithelium. Early in embryonic life, epithe- 

 lial buds or strings of epithelial cells grow down into the 

 ovary. Soon these buds lose their connection with the 

 germinal epithelium and form small groups or nests of 

 cells. These groups or nests of cells are known as young 

 Graafian follicles. In each follicle one cell takes a central 

 position and is destined to form the egg or ovum. The 

 egg increases rapidly in size, receiving protection and 

 perhaps nourishment from the cells which surround it. 

 The cells which surround the egg are known as follicular 

 cells. 



In the section of the cat ovary, find a young Graafian 

 follicle, draw it, and label all the parts. 



Only a small number of the young ova ripen and are 

 discharged as mature ova. Those which mature do so 



