PINNA. 301 



in the water. This they possess in common with the Mussel. 

 But instead of a hundred undivided parallel and flattened 

 fibres^ terminated by a circular gland^ furnished with 

 absorbents, and growing from the body of the animal, we 

 have here a machine as incontestably mechanical as that of 

 a wire-drawer^s mill. The Pinna is provided with an ex- 

 tensile member Hke a finger, and this contains a glue, 

 whicli the animal protrudes at pleasure, by means of a variety 

 of minute perforations in the tip. This glue, or gum, as 

 in the instance of the common spider or the silkworm, 

 having passed through these apertures, becomes threads 

 of almost inperceptible fineness; and these, when joined, 

 compose the silk which is so much valued by the Sici- 

 lians. But the animal first attaches the extremity of the 

 thread, by means of its adhesive quality, to some crag 

 or pebble of unusual size ; and when this is effected, the 

 Pinna, receding from that point, draws out the thread 

 through the perforation of the extensile member by a pro- 

 cess which Paley, in describing the similar operations of 

 the terrestrial silkworm, justly compares to the drawing 

 of wire. One difference alone exists. The wire is the 

 metal unaltered, except in figure ; whereas, in the forming 

 of the thread, the nature of the substance is somewhat 



