INTERNAL ANATOMY OF INSECTS. 13t 
fect upon it to melt or soften it: indeed, without these 
qualities it would be of no use to us?.. As soon as it 
leaves the spinneret it becomes the thread we call silk, 
which being drawn through ¢wo orifices is necessarily 
double through its whole length. This thread varies consi- 
derably in colour and texture, as has been before stated®, 
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 serzcterzum 
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 between silk and 
varnish, which it spins, not in a thread, but in a broad 
riband¢. 
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- 
sion I observed to you that many predaceous, carnivorous, 
" N, Dict. d’ Hist. Nat. vi. 305. » Vor. Il. p= 221—- 
© 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—. ° Reaum. v. 24. 
Kee, 
