Centrioles are cylindrical structures found in animal cells and play a crucial role in cell division. Typically, each centriole is made up of nine sets of triplet microtubules arranged in a circular pattern, resembling a small barrel or a pair of straws. When viewed under an electron microscope, centrioles appear as distinct, structured shapes, often appearing in pairs that are oriented at right angles to each other.
Structurally, each centriole is about 400-500 nanometers in length and around 200 nanometers in diameter. The precise arrangement of microtubules is important for their function in organizing the spindle fibers during cell division. Centrioles also play a role in forming cilia and flagella in certain types of cells, which are important for movement and sensation in various organisms.