INSECTS : THEIR MOUTHS. 157 



" the windows at which the [silkworm's] soul looks 

 through " — provided he has any soul ; in prosaic par- 

 lance, his eyes. 



Now, having thus introduced the several members of 

 our useful friend's physiognomy to you, let me call your 

 attention to a fleshy wart just beneath the lower lip, and 

 midway between the bases of the two fore legs. This 

 wart terminates in a horny point not unlike a bird's beak, 

 which is perforated, and from the tip of which the glisten- 

 ing yellow filament of silk is ever drawn out, as the cater- 

 pillar throws his head from side to side. This pointed 

 wart is the spinning organ ; and the thread of silk is, 

 as it issues from the orifice, a fluid gum, which hardens 

 immediately on its exposure to the air. The silk gum is 

 secreted by the caterpillar in two long blind tubes, which 

 lie twisted and coiled in the interior of the body, occupy- 

 ing nearly the whole space, except that which is taken 

 up by the great digestive canal. These become very 

 slender as they approach the head, and at length termi- 

 nate in a reservoir, which opens by the little pointed 

 wart which you have just seen. 



Many caterpillars are able to suspend themselves at 

 pleasure by means of the thread which they are spinning, 

 lengthening it and "stopping it off," at will. This latter 

 operation they perform (though they cannot recal the 

 thread when once it has issued) by means of an angular 

 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 colourless in the reservoir; but, as it issues forth, 

 it becomes 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 discharged from it in the manufacture. 



