86 AN INTRODUCTION TO ZOOLOGY 



fairly clear, staining but lightly and containing a well-marked 

 nucleolus. In certain very large nerve cells a system of tiny canals 

 seems to be present in the cytoplasm, and it is thought they conduce 

 to the ready removal of waste products and to the supply of 

 nutriment. 



One of the processes leaving the cell differs in function from the 

 rest ; it takes nervous messages away from the cell and is termed the 



FIG. 28. Diagram of a multipolar nerve cell from the spinal 

 cord of an ox. 



A., axon ; D., dendron ; N., nucleus ; T., tigroid substance. 



axon or neuraxis. In many cases it differs also in structure, for it 

 forms a long, in some parts enormously long strand of fibrillar proto- 

 plasm of practically uniform diameter. During its course it gives 

 off a certain number of very delicate fibrils, the collaterals, and finally 

 finishes up in a little tuft of twigs known as the terminal dendrite. 

 This is always the case in cells whose fibres leave the spinal cord and 

 pass out into the tissues, and they may be long enough to run right 

 from the cord to the tips of the toes. If, on the other hand, the cell 

 remains within the central nervous system, the axon is generally 

 not nearly so long and resembles more closely the other processes, 

 and its terminal dendrite is often more spread out. 



