THE RAT-TAILED WORM FLY. 44I 



air, which are visible to the naked eye, and imme- 

 diately repair to the surface for fresh supplies. 



So anxious is nature to provide animals in every 

 state of their existence with air that, after the trans- 

 formation of many insects into crysalids, she creates 

 instruments for that purpose, which did not exist 

 previous to their transformation. These Rat-tailed 

 Worms, soon after they are transformed into chry- 

 salids, instead of a soft pliable skin, are covered 

 with a hard crustaceous substance, seemingly im- 

 pervious to the air ; and the tail, which was the 

 wind-pipe 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 under part of what was the head of the animal. 

 These horns, which are hard and tubular, M. de 

 Reaumur discovered to be real wind-pipes, destined 

 for the introduction of air into the chrysalis - 3 a state 

 in which many animals have the appearance of 

 being dead, and, of course, should seem to have 

 little use for respiration. He likewise discovered 

 that these horns, which had pierced the hard exte- 

 rior covering, terminated in as many tracheae in the 

 body of the animal. This fact affords a strong 

 example of the necessity of air for sustaining 

 the principle of life, even in its lowest condition. 

 After these animals pass from the chrysalis state to 

 that of flies, they are deprived both of their tails 

 and horns. But nature, in this last stage of their 

 existence, has not left them without proper re- 

 sources for the introduction of air into their bodies. 

 Instead of protuberant tracheal in the form of tails 



