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Respiration
Spiders have a very complex respiratory system in that it has two separate systems, the book lungs and the trachea (tiny tubes that penetrate into the body). The book lungs in the spider are not very efficient. Large spiders have a 50 beat per minute heart rate. Smaller spiders have a faster heart beat at about 100 beats per minute. Most arachnids exchange gasses the way humans do by taking in oxygen and releasing carbon dioxide. Gases move in and out of the book lungs, which are layers of tissue called lamellae. Spiracles are holes in the exoskeleton that helps arachnids to breathe. The exoskeleton is made of hard, lightweight, non-living material that covers the outside of the arachnid.
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