17 o Additions to the hnoivledge of Silk. [No. 3, 



which I have yet been able to effect a separation is by tearing the 

 silk gently with fine bent needles. In this way, small portions have 

 been opened out, and the compound nature of the filament placed be- 

 yjond a doubt. I have been able to measure the diameter of the 

 filaments, not very accurately, however, on account of their trans- 

 parency, but the finest do not exceed 35^0 o th of an inch * 



It is scarcely prudent to speculate upon the kind of organ by which 

 this silk is produced, there is, however, reason to believe, that the silk 

 issues in the form of a hollow, or ribbed cylinder, of which the 

 opaque ribs are the primary filaments, and the interspaces the cement. 

 Such a cylinder, while in a soft state, would collapse, as soon as the 

 central support was withdrawn, and its application to a leaf, or a 

 part of the cocoon already spun, would cause it to be flat. This of 

 course is only surmise, and is only given as a hint to any one who 

 may have the means and inclination to pursue the enquiry. It can 

 only be demonstrated by a careful preparation of the spinning organs 

 of the caterpillar which, if I have guessed rightly, will be found in 

 the form of a ring of minute apertures set round a central papilla. 



The silk of the Actias selene is flat like Tussah silk, and from its 

 fibrous appearance, there can be little doubt that it also is compound. 

 That of Attacus atlas appears to be cylindrical, it is, however, finely 

 grooved on the surface, and is in all probability a compound structure 



like the other two. 



I have examined several kinds of silk, and have invariably found it 

 to consist of two filaments, simple or compound, as the case may be,: 

 placed side by side. I mention this because in all the works save one, 

 to which I have been able to refer the silkworm is said to spin a 

 single thread. The exception is " Adam's Essays on the Microscope." 

 Edition of 1798. It is there correctly stated that the filament is 

 double. 



