OF NATURAL HISTORY. 433 



equally diverfiiied as thofe of the inhabitants of different 

 nations and climates. Some, like particular favages, con- 

 ftrucl a kind of hammocks, in which they take their victuals, 

 repofe, and fpend their lives till the period of their trani- 

 formation. Others, like the Arabs and Tartars, conftru^t 

 and live in filken tents, and, after confuming the neighbour- 

 ino- herbage, they leave their former habitations, and encamp 

 on frefh pafture. Under thefe tents they are not only pro- 

 tefted from the injuries of the weather, but they repofe in 

 them when fick, or in a ftate of inactivity. They go out of 

 their tents at particular times in queft of food, and bften to 

 confiderable diftances ; but they never lofe their way back. 

 It is not by fight that they are directed with fo much cer- 

 tainty to their abodes. Nature has furniflied them with 

 another guide for regaining their habitations. We pave our 

 ftreets with ftones ; but the caterpillars cover all their roads 

 vvith filken threads. Thefe threads make white tracks, 

 which are often more than a fixth of an inch wide. It is 

 by following thefe filken tracks, however complicated, that 

 the caterpillars never mifs their nefls. If the road is broke 

 by a man's finger drawn along it, or by any other accident, 

 the caterpillars are greatly embarrafTed. They flop fudden- 

 ly at the interrupted fpace, and exhibit every mark of fear 

 and of difHdence. Here the march flops, till an individual; 

 more bold or more impatient than his companions, travcrfes 

 the gap. In his pailage, he leaves behind him a thread of 

 filk, which ferves as a bridge or condu6lor to the next that 

 follows. By the progreflion of numbers, each of which 

 fpins a thread, the breach is foon repaired. We cannot fup- 

 pofe that thefe flupid animals cover their roads to prevent 

 their wandering. But they never wander, becaufe their 

 roads are covered with filk. In this, as well as in many 

 other inflances. Nature obliges animals to embrace the mod 

 effedlual means of felf-prefcrvation, and even of conve- 



