INSECTS: THEIR MOUTHS 185 



point formed by the two slender tubes at their junction 

 in the reservoir; thus compressing the thread of gum, and 

 so preventing any more from issuing. The gum is per- 

 fectly colorless in the reservoir, but as it issues forth be- 

 comes coated with a varnish, which is secreted in the same 

 organ, and which is poured out at the same time. In the 

 case of the common Silkworm, this varnish imparts to the 

 silk that brilliant yellow hue which it generally possesses, 

 and which, as the varnish is soluble, can be easily dis- 

 charged from it in the manufacture. 



