SILK. 



169 



TABLE of the Diameter, Strength, and Tension of a Single Cocoon Thread or 

 Bave, and Dimensions of Cocoons of the chief Mulberry and Indian Wild 

 Silks. By Sir Thomas Wardle, F.G.S., F.C.S. 



Entomologists have distinguished a good many species of silk-moths 

 whose larvae, after feeding up, protect themselves by a continuous silky 

 thread spun into a covering of an oblong shape which completely en- 

 closes the caterpillar. This outer covering has been termed the cocoon. 



The world's produce of animal silk is dependent upon the amount 

 that is contained in the cocoons of the cultivated species of silkworms. 

 Wild silks are the product of the cocoons that have been produced by 

 feral silkworms. 



The most valuable silk of commerce is that produced by the silk- 

 worm of Bombyx mori. The specific name signifies that the caterpillar 

 feeds upon the leaves of the mulberry tree. When pressed for food,. 

 the insect will feed upon the leaves of the garden lettuce (Lactuca sativd) y 

 but the silk produced is of an inferior quality. 



The outer covering of the cocoon is composed of a kind of fluffy silk 

 sometimes termed floss ; this is used as spun silk, and forms an important 

 and separate branch of the silk industry under the name of waste silks. 



