70 INSECT MANUFACTURES. 



is a spider which forms a spherical cocoon for its 

 eggs, an inch in diameter, of a yellow silk, which 

 the inhabitants spin on account of the permanency 

 of the colour. It must also be observed that the 

 silk of spiders is useful to the astronomer, who 

 employs the strongest thread (the one, namely, 

 which supports the web) for the divisions of the 

 micrometer. By its ductility, this thread acquires 

 about a fifth of its ordinary length. 



