MECHANICS OF RESPIRATION 



they stretch it out in the surrounding water, to fulfil 

 its proper function; and, at the least alarm, fetch 

 it in again hurriedly into their tube. Others, 

 closely related, behave in the same way; they spread 

 out their handsome branchial plume, rolled up in a 

 spiral, inlaid with violet and white, leave it extended in 

 the water, and stay without moving until the moment 

 when, for some reason or other, everything is hastily 

 withdrawn, and nothing is to be seen except the outside 

 of the tube in which the animal lives. 



Going still further down the scale, in even more 

 simple creatures like the lower worms, the jelly-fish, and 

 the sea-anemones, there is not even this. The respira- 

 tory function, instead of being localized in specially 

 constructed gills, has no specific organ; it is carried 

 out directly over the surface of the body. In this 

 case, since there is no apparatus, the movements 

 proper to its mechanism do not exist, and, since 

 there is no reason for its existence, we see nothing 

 of this mechanism of respiration. 



However, this does not prevent its taking place in 

 many aquatic animals, large and small. In it the world 

 of waters has a mode of behaviour, a sort of moving 

 condition, which we hardly ever find in the world of 

 land and air creatures. There are continual plays of 

 expression, which the requirements of respiration render 

 necessary, which compel individuals to carry them out, 

 water being denser to move than air. We have only 

 to look in an aquarium, and there we find the majority 

 of creatures going through these movements, which 

 are more obvious to us than they are in the corre- 

 sponding animals which breathe in air. The masses 

 of the waters, the vast areas of the sea bed, are peopled 

 by animals continually showing movements which are 

 ordained by the needs of their respiration. Besides 

 movements of locomotion and prehension, they show 

 us also gestures of respiration, more apparent and more 

 varied than we ever find elsewhere. 



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