RESPIRATION. 93 



Rondeletius made many experiments on this subject. If, says 

 he, fishes are put into a narrow-mouthed vessel filled with 

 water, and a communication with the air be preserved, the 

 animals live, and swim about, not for days and months only, 

 but for several years. If the mouth of the vessel, however, 

 be closely shut, either with the hand or any other covering, 

 so that the passage of the air is excluded, the fishes suddenly 

 die. Immediately after the mouth of the vessel is closed, the 

 creatures rush tumultuously, one above another, to the top, 

 contending which of them shall soonest receive the benefit of 

 the air. In the shallow parts of rivers, when frozen, many 

 fishes are found dead. But, when parts of a river are deep 

 or rapid, the fishes fly from the ice, and by this means avoid 

 destruction. 



These, and similar experiments, have been repeated by Mr. 

 Willoughby and jnany other modern authors ; and they have 

 uniformly been attended with the same .event. A carp, in a 

 large vessel full of water, was placed in the receiver of an air- 

 pump. In proportion as the air was exhausted by working 

 the pump, the surface of the animal's body was covered with 

 a number of bubbles. The carp soon breathed quicker, and 

 with more difficulty. A little after it arose to the surface in 

 quest of air. The bubbles on its surface next disappeared ; 

 the belly, which before was greatly swollen, suddenly col- 

 lapsed ; and the animal sunk to the bottom, and expired 

 in convulsions. 



* Air is distributed in the bodies of Insects by a great 

 number of tubes or canals, called trachea, which convey it to 

 every part. These communicate with the external air by 

 means of openings called stigmata, which furnish a constant 

 supply. That these organs are destined for the transmission 

 of air, has been proved by repeated experiments ; for when 

 stopped up by the application of oil, or other unctuous sub- 

 stances, the animals soon lose their existence. In some 

 insects they protrude externally to some distance from the 

 body, and have the appearance of one, two, or three tails; and 

 in others they arise from the back and sides.' 



In contemplating the parts of animals, when the uses of 

 these parts are not apparent, we are apt to deceive ourselves 

 by rashly supposing them to answer purposes for which they 

 were never intended by nature. Impressed with this idea, 

 M. de Reaumur was not satisfied with the notion of Godart 

 and others, that the long tails of certain worms were intended 

 to keep them steady in their motions, and prevent them 



