284 NATURAL HISTORY. [cH. XVt, 



Other caterpillars place themselves in attitudes 

 Avhich present a very formidable appearance, and 

 although perfectly harmless, make a very disgreeable 

 impression upon the mind. The caterpillar of a 

 hawk-moth, when in a state of repose, assumes the 

 position of the sculptured sphinx. 



Most of the surveyors possess a contrivance for 

 transporting themselves from one place to another, 

 which must not be overlooked : wherever they ad- 

 vance, they fix a silken cord ; hence their track is 

 constantly marked by a line of silk. The use of 

 this provision becomes immediately apparent when- 

 ever the leaf or twig on which they are found hap- 

 pens to be shaken. The creature drops from its 

 place, and would fall quite to the ground, if it did 

 not possess the means of suspending itself; but it 

 is furnished with spinners, which secrete silken 

 matter, and it possesses also the faculty of giving 

 out as much of this substance as may be required 

 for its purposes ; it seems to have a sphincter for 

 this especial object. By means of a silken appara- 

 tus thus prepared, it is enabled at any time to descend 

 from the top of a high tree, and mount again, without 

 undergoing the fatigue of climbing up the twisted 

 branches; the descent is regulated by the wishes 

 and purposes of the insect, rapid or slow as may be 

 required ; and if necessaiy, its descent may be in- 

 stantly arrested, and the animal may remain for any 

 length of time suspended in mid-air. The two an- 

 nexed figures will explain the mechanism of these 

 proceedings. In the first, the creature is seen sus- 

 pended by its thread ; in the second, it is represented 

 in the act of mounting: for the latter puipose, it 

 seizes the silken cord between its two teeth, and 

 curving up that portion of its body, in which its six 

 true legs are situated, it lays hold of the cord with 

 the last two pair ; this secures to it another fixed 

 point ; it th-^n lifts up its head a second time, lays 

 hold of an additional piece of the silk ; and by a 



