OF NATURAL HISTORY. 121 



furface of the water or mud in which they are placed. Thefe feathers 

 prevent the water from entering into the tube, or organ of refpira- 

 tion ; and, when the animal raifes the termination of its body to the 

 furface, in order to receive air, it ere£ls and fpreads the feathers, 

 and by this means expofes the end of the tube to the atmofphere. 

 When cautioufly cut open, two large vefTels, or tracheae, appear on 

 each fide, and occupy almoft one half of the body. Both of thefe 

 wind-pipes terminate in the open tube, or laft ring. Though thefe 

 worms are furniflied with organs of refpiration, and adually refpire 

 air, yet M. de Reaumur difcovered that fome of them could live 

 more than twenty-four hours without refpiration. 



So anxious is Nature to provide animals, in every ftate of their 

 cxiftence, with air, that, after the transformation of many infedts 

 into chryfalids, fhe creates inftruments for that purpofe, which did 

 not exifl, previous to their transformation. The rat- tailed worms, 

 formerly mentioned, foon after they are transformed into chryfalids, 

 inftead of a foft pliable fkin, are covered with a hard cruftaceous 

 fubftance, feemingly impervious to the air ; and the tail, which was 

 the wind-pipe of the animal in its firft ftate, gradually vanifhes. In 

 a few hours, however, four hollow horns ftioot out, two from the 

 fore, and two from the hind, part of what was the head of the ani- 

 mal. Thefe horns, which are hard and tubular, M. de Reaumur 

 difcovered to be real wind-pipes, deftined for the introdudion of air 

 into the chryfalis, a ftate in which the animals have the appearance 

 of being almoft totally dead, and, of courfe, fhould feem to have 

 little ufe for refpiration. He likewife difcovered that thefe horns, 

 which had pierced the hard exterior covering, terminated in as many 

 tracheae in the body of the animal. This fadt affords a ftrong ex- 

 ample of the neceflity of air for fuftaining the principle of life, even 

 in its loweft condition. After thefe animals pafs from the chryfalis 

 ftate to that of flies, they are deprived both of their tails and horns. 

 t Q^ But 



