SPINNING CATERPILLARS. 311 



Labium or loxL-vr Up of Casus.— a. Silk-Hilje. 



are like a pair of distaffs for spinning the gum into a 

 silken thread. She fixes the first drop of gum that 

 issues where she pleases, and tlien draws back her 

 head, or lets herself fall, while the gum continuing 

 to flow, is^ drawn out and lengthened into a double 

 stream. Upon being exposed to the air, it imme- 

 diately loses its fluidity, becomes dry, and acquires 

 consistence and strength. She is never deceived in 

 adjusting the dimensions of the [united] apertures, 

 or in calculating the proper thickness of the thread, 

 but invariably makes the strength of it proportion- 

 able to the weight of her body. 



"■ It would be a very curious thing to know how 

 the gum which composes the silk is sepaiated and 

 drawn off' from the other juices that nourish the 

 animal. It must be accomplished like the secre- 

 tions formed by glands in the human body. I am 

 therefore persuaded that the gum-bags of the silk- 

 w^orrn are furnished with a set of minute glands, 

 which, being impregnated with gum, afford a free 

 passage to all the juices of the nuilberry-leaf corres- 



