Answer
Discovery
               In 1928 Kotlzuf observed a network of fibers extended through out the cytoplasm with hep of light microscope. It was confirmed by Cohen when studying it under electron microscope in 1972.
Structure
             It is a network of protein fibers that extend through out the cytoplasm. It is also called as skeleton of cytoplasm.  
Composition
             It is composed of different types of proteins, like actin, troponin, myosin etc.  
Types
          Cytoskeleton is of three types, these are
1. Micofilaments
2. Microtubules
3. Intermediate filaments.
Function
1. Cyclosis
               It is the streaming movement of cytoplasm which is controlled by cytoskeleton. It help in the transport of different organelles like ribosome and mitochondria to those area where they are needed.
2. Amoeboid movement
              Cytoskeleton help in amoeboid movement through which amoeba move towards sunlight or any other thing needed as food.
3. Maintain cell shape
             Cytoskeleton help in maintaining shape of cell.
4. Spindle fibers
           Cytoskeleton also help in the assembly and disassembly of spindle fibers during cell division.