INTERNAL ANATOMY OF INSECTS. 137 



but in the most active solvents, and even heat has no ef- 

 fect upon it to melt or soften it : indeed, without these 

 qualities it would be of no use to us a . As soon as it 

 leaves the spinneret it becomes the thread we call silk, 

 which being drawn through two orifices is necessarily 

 double through its whole length. This thread varies 

 considerably in colour and texture, as has been before 

 stated 5 , and sometimes resembles cotton or wool rather 

 than silk. In spiders it is of a much softer and more 

 tender texture than that of other spinning insects ; and 

 Mr. Murray seems to have proved that it is imbued, in 

 the case of the gossamer, with negative electricity : in 

 the sericterium the fluid that produces it is sometimes 

 white or grey, and at others yellow . A remarkable 

 gnat (Ceroplatus tipuloides), living on an agaric, carpets 

 its station of repose and its paths with something be- 

 tween silk and varnish, which it spins, not in a thread, 

 but in a broad riband d . 



ii. Saliva. Many insects have the power of discharg- 

 ing from their mouth a fluid which seems in some degree 

 analogous to the saliva of larger animals. Thus many, 

 as Lepidoptera, Hemiptera, Diptera, &c., can dilute 

 their food, and render it fitter for deglutition. I have 

 seen a common fly when not employed in eating, emit a 

 globule of fluid as big as a grain of mustard-seed from 

 its proboscis, and retract it again. On a former occa- 



a N. Diet. d'Hist. Nat. vi. 305. b VOL. III. p. 221. 



c Treviran. Arachnid. 44. In Paraguay a spider is found which 

 makes spherical cocoons of yellow silk, which are spun because of 

 the permanence of the colour. This operation occasions a flow of 

 water from the eyes and nose of the spinners. Azara Voyag. 212. 

 See also Murray in Werner. Trans. 1823. 8. d Reaum. v. 24. 



