DR KEITH WHEELER / SCIENCE PHOTO LIBRARY DR KEITH WHEELER / SCIENCE PHOTO LIBRARY
Silkworm tracheae. Phase contrast light micrograph of the shed skin of a silkworm (Bombyx mori) caterpillar, showing the tracheae and spiracle holes that form an insect's respiratory system. The spiracles (right) are the openings to the tracheae (airways, left), which branch throughout the caterpillar's body. Tracheae are continuous with the epidermis, and are thus made of chitin, and reinforced with bands of chitin. The tracheae branch into smaller units (tracheoles) to reach the cells, allowing oxygen to diffuse in and carbon dioxide to diffuse out. Magnification: x37 when printed at 10 centimetres wide.
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