SILK-PRODUCING INSECTS. 



are, perhaps, of all animals, those 

 which have proved most useful to man. The 

 silkworm alone, the most important of them all, 

 has been, in a practical point of view, the object 

 of more experiments than any other known creature. 

 Volumes have been written upon it, new varieties are 

 constantly being discovered and reared with hopes of 

 realizing still greater advantages, and, at the same 

 time, investigations are pursued with a view of in- 

 creasing the produce of the original insect. 



The chemical nature of silk, which is secreted 

 through the mouth of the grub from organs resem- 

 bling the salivary glands of other animals, is very 

 little known. In the body of the silkworm it 

 appears as a viscous liquid, which becomes solid 

 when in contact with the air. If we take a silk- 

 worm at the period when he is about to spin his 

 cocoon, and immerse him for twelve hours in vine- 

 gar, on opening the reservoir which contains the 

 liquid silk, the latter may be drawn out into threads 

 as thick as a common sized knitting-needle, and of 

 such tenacity that it is impossible to break them 



