Egg cell 
Sperm cell 
The variety oftffisfman cells. After 
fertilization by a sperm, a single 
human egg cell divides again and 
again into many kinds of special- 
ized cells whose structures vary 
according to the functions they fill. 
Some nerve cells, for example, are 
3 feet long to reach from spine to 
toe. The orderly structure of typical 
skeletal muscle is shown here in 
such detail that if the entire muscle 
cell were drawn to the same scale 
as the fragment shown, it might be 
1 ,000 feet long. 
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