Spiracle

No, he breathes through his spiracle alone; and this is on the top of his head.

If I say, that in any creature breathing is only a function indispensable to vitality, inasmuch as it withdraws from the air a certain element, which being subsequently brought into contact with the blood imparts to the blood its vivifying principle, I do not think I shall err; though I may possibly use some superfluous scientific words. Assume it, and it follows that if all the blood in a man could be aerated with one breath, he might then seal up his nostrils and not fetch another for a considerable time.