MECHANICS OF RESPIRATION 



This expression is not everywhere the same. If, as 

 most frequently happens, it consists of yawnings of 

 the mouth and flappings of the gill-covers, it is mani- 

 fested elsewhere in many other ways. It varies accord- 

 ing to its structure, although the result, the constant 

 renewing of the water, is always sought. In this 

 diversity there is sufficient material for a chapter on 

 physiology, which I can only deal with in a short 

 sketch, based upon my observations in the aquarium. 



The gurnards, with thick armoured cheeks the 

 compactness and hardness of which extend to the 

 gill-covers, cannot swell the mouth with water as the 

 scorpion- or hog-fish do; their mask remains im- 

 movable, the lips slightly parted, and the mouth half 

 open. But their throat palpitates continually; it 

 expands and contracts alternately, producing motions 

 of inspiration and expiration, because the roof of the 

 mouth rises and falls as it inhales the water and sends 

 it to the gills. Beside them, almost buried in the 

 sandy bottom, the soles, motionless, display only that 

 side of their heads which has the eyes. The gill- 

 cover is behind, quite near. We see it rise and fall 

 to effect the expiration, sometimes partially uncovering 

 the gills, sometimes covering them, following a rhythm 

 of 30 to 35 beats a minute. Inspiration is effected by 

 the corner of the mouth, which is kept open in a kind 

 of permanent gape, the other parts of the lips remaining 

 closed. 



The eels, congers and murry, have other peculiarities. 

 In these creatures, the neck swells and collapses alter- 

 nately, breathing in the water which penetrates through 

 the slightly opened mouth, and breathing it out again 

 through the gill-slits after it has passed over the gills. 

 The wave of swelling begins at the back of the head, 

 extends progressively to the neck and throat, then 

 ceases and begins again with the same rhythm. The 

 fish, lurking in the hollow of a rock or buried in the 

 mud, only allows its head and neck to appear. There 

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