94 RESPIRATION 



from rolling. Reaumur observed, that these worms or grubs 

 could lengthen or shorten their tails at pleasure, but that they 

 were always longer than the animal's body. Because these 

 tails have some resemblance to that of a rat, he distinguishes 

 the animals by the name of rat-tailed worms. These worms 

 are aquatic, and never appear on dry ground till they are 

 about to undergo their first transformation. Reaumur, in 

 order to observe their economy more closely, collected a 

 number of rat-tailed worms, and put them into a glass vessel 

 filled two inches high with water. At first they were consid- 

 erably agitated, each seemingly searching for a proper place 

 of repose. Some of them swam across, others attached 

 themselves to the sides, and others rested at the bottom of the 

 vessel. In a quarter of an hour they were almost entirely 

 tranquil, and Reaumur soon discovered the real use of their 

 long tails. Upon examining the vessel, he found that each of 

 the animals, in whatever situation they were placed, extended 

 its tail exactly to the surface ; that, like other aquatic in- 

 sects, the respiration of air was necessary to their existence ; 

 and that the tail, which is tubular, and open at the extremity, 

 was the organ by which this operation was performed. Jri 

 this experiment, the distance from the bottom to the surface 

 was two inches, and, of course, the tails were of equal length. 

 To discover how far the animals could extend their tails, he 

 gradually augmented the height of the water, and the tails 

 uniformly rose to the surface, till it was between five and six 

 inches high. When the water was raised higher, the animals 

 immediately quitted their station at the bottom, and either 

 mounted higher in the water, or fixed upon the sides of the 

 vessel, in situations which rendered it convenient for them to 

 reach the surface with the points of their tails. These tails 

 consist of two tubes, both of which are capable of extension 

 and contraction. The first tube is always visible ; but the 

 second, which is the proper organ of respiration, is exerted 

 only when the water is raised to a certain height. Through 

 this tube the air is conveyed into two large tracheae or wind- 

 pipes within the body of the animal, and maintains the prin- 

 ciple of life. When the tails are below the surface, they 

 occasionally emit small bubbles of air, which are visible to 

 ihe naked eye : and immediately are extended to the surface 

 for fresh supplies. These worms pass the first and longest 

 part of their lives under water; when near the time of their 

 transform ation, they leave the water, go under the ground, 

 and are there transformed into chrysalids ; and, lastly, from 



