RESPIRATION. 95 



this state they are transformed into flies, and spend the re- 

 mainder of their existence in the air. 



Another species of aquatic worms merits attention. They 

 frequent marshes, ditches, and stagnating waters. Their gen- 

 eral color is a greenish brown. T-heir bodies consist of 

 eleven rings; and their skin is not crustaceous, but rather 

 resembles parchment. Though these animals, before their 

 transformation into flies, live in water, air is necessary to sup- 

 port their principle of life ; and the apparatus with which 

 nature has furnished them for that important purpose, deserves 

 our notice. The last ring or termination of their bodies is 

 open, and serves as a conductor of air. From this last ring 

 proceeds a number of hairs, which, when examined by the 

 microscope, are found to be real feathers with regular varies. 

 In particular situations, they bend the last ring in such a 

 manner as to reach the surface of the water or mud in which 

 they are placed. These 'feathers prevent the water from en- 

 tering into the tube, or organ of respiration ; and, when the 

 animal raises the termination of its body to the surface, in 

 order to receive air, it erects and spreads the feathers, and 

 by this means exposes the ends of the tube to the atmosphere. 

 When cautiously cut open, two large vessels, or trachea, ap- 

 pear on each side, and occupy almost one half of the body. 

 Both of these windpipes terminate in the open tube, or last 

 ring. Though these worms are furnished with organs of res- 

 piration, and actually respire air, yet M. de Reaumur discov- 

 ered that some of them could live more than twenty-four 

 hours without respiration. 



So anxious is Nature to provide animals, in every state of 

 their existence, with air, that, after the transformation of many 

 insects into chrysalids, she creates instruments for that pur- 

 pose, which did not exist previous to their transformation. 

 The rat-tailed worms, formerly mentioned, soon after they 

 are transformed into chrysalids, instead of a soft, pliable skin, 

 are covered with a hard, crustaceous substance, seemingly 

 impervious to the air ; and the tail, which was the windpipe 

 of the animal in its first state, gradually vanishes. In a few 

 hours, however, four hollow horns shoot out, two from the 

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

 animal. These horns, which are hard and tubular, are discov- 

 ered to be real windpipes, destined for the introduction of 

 air into the chrysalis, a .state in which the animals have the 

 appearance of being almost totally dead, and, of course, 

 would seem to have little use for respiration. It is likewise 



