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 nucleolus 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. It is from this germinal epi- 

 thelium that the eggs are formed. Early in embryonic 

 life, epithelial 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 fo'^m 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 



