CELL STRUCTURE 



15 



contains a still smaller body, or minute point, called the 

 nudeolus. 



6. The yolk of a common hen's egg probably illustrates this 

 best. If we break the egg into a saucer, being careful not to 

 break the yolk, we shall find upon examination that the yolk 

 is held together by a thin and delicate membrane, the cell 

 wall. The liquid portion of the yolk is the protoplasm. And 

 we can also ^readily see, upon careful inspection, a compara- 

 tively small speck, more opaque, or rather whitish in ap- 

 pearance, which is the nucleus. The nucleolus cannot be 

 observed by the naked eye. The following diagram of the 

 yolk will illustrate these facts : 



d, Nucleolus. 

 c, Nucleus. 



b, Protoplasm, 

 a, CellWalL 



7. Cell Reproduction. The following series of diagrams 

 shows how simple the process of cell reproduction is. In a 

 we have a simple cell ; in & it has changed its shape by elon- 

 gating and constricting in its centre; in c the same process 

 has been continued; and in d we have two new cells, but no 

 parent. The identity of the parent has been lost in its off- 

 spring. 



8. Cell Nourishment. The. cell wall absorbs nourishment, 

 which soon becomes a part of the general protoplasm. Waste 

 products in a similar manner are expelled through the cell 

 wall. Some cells have the power of excreting from their food 



6. Describe the four parts of a cell. 7. Describe the process of cell reproduction. 

 A. How is nourishment obtained ? Waste products expelled ? 



