OF NATURAL HISTORY. 119 



application of oil, or other unftuous fubftances, the animals foon 

 lole their exillence. 



In contemplating the parts of animals, when the ufes of thefe parts 

 are not apparent, we are apt to deceive ourfelves by rafhly fuppo- 

 fing them to anfwer purpofes for which they were never intended 

 by Nature. Impreffed with this idea, M. de Reaumur was not fa- 

 tisfied with the notion of Goedart and others, that the long tails cf 

 certain worms were intended to keep them fteady in their motions, 

 and to prevent them from rolling. Reaumur obferved, that thefe 

 worms or grubs could lengthen or fliorten their tails at pleafure, but 

 that they v/ere always longer than the animal's body, Becaufe thefe 

 tails have fome refemblance to that of a rat, he diftinguiflaes the ani- 

 mals by the name of rat-tailed ivorms. Thefe worms are aquatic, 

 and never appear on dry ground till they are about to undergo their 

 firft transformation. Reaumur, in order to obferve their oeconomy 

 more clofely, colledted a number of rat-tailed worms, and put them 

 into a glafs veflel filled two inches high with water. At firft they 

 were confiderably agitated, each feemingly fearching for a proper 

 place of repofe. Some of them fwam acrofs, others attached them- 

 felves to the fides, and others refted at the bottom of the vefTel. In 

 a quarter of an hour they were almoft entirely tranquil, and Reau- 

 mur foon difcovered the real ufe of their long tails. Upon exami- 

 ning the veflel, he found that each of the animals, in whatever fitua- 

 tion they were placed, extended its tail exadly to the furface ; that, 

 like other aquatic infeds, the refpiration of air was neceflary to their 

 exiftence; and that the tail, which is tubular, and open at the extre- 

 mity, was the organ by which this operation was performed. In 

 this experiment, the dillance from the bottom to the furface was two 

 inches, and, of courfe, the tails were of an equal length. To dif- 

 cover how far the animals could extend their tails, this moft inge- 

 nious and indefatigable phllofopher gradually augmented the height 



