Light micrograph of a piece of woven silk fabric. The threads, an example of a protein fibre, are obtained from the cocoon spun by the larva of the silk moth Bombyx mori. Two silk glands running the length of each caterpillar extrude a semi- liquid mixture which hardens on contact with the air. All lepidopteran caterpillars produce a form of silk in the same way, but none has the same quality as that produced by Bombyx mori. Each cocoon yields a single filament up to 1. 6 kilometres long, yet over 100 of them are required to produce a single silk neck-tie. Magnification: x100 at 35mm size.