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<p>general each segment of the body can have only one pair of spiracles, each of which connects to an atrium and has a relatively large tracheal tube behind it. The tracheae are invaginations of the cuticular <a href="page.php?w=exoskeleton">exoskeleton</a> that branch (<a href="page.php?w=anastomosis">anastomose</a>) throughout the body with diameters from only a few micrometres up to 0.8&nbsp;mm. The smallest tubes, tracheoles, penetrate cells and serve as sites of <a href="page.php?w=diffusion">diffusion</a> for <a href="page.php?w=water">water</a>,</p><p>
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