VISION IN INSECTS* 133 



cause has ceased, prolonging the sensation of light 

 (especially of a vivid one) for an instant in the eye. 

 We may thus conceive the possibility of other ani- 

 mals, such as insects, incapable of being affected with 

 any of our colours, and receiving their whole stock of 

 luminous impressions from a class of vibrations alto- 

 gether beyond our limits, as Dr. Wollaston has inge- 

 niously imagined (we may almost say proved) to be 

 the case with their perceptions of sound*." 



This view of the matter is certainly beautiful and 

 plausible, though, in the present state of our know- 

 ledge, we can only admit it as a theory. 



The vision of insects has been recently investi- 

 gated with great minuteness by Professor Miiller, of 

 Bonn t> an excellent account of whose researches 

 has been given by Mr. Parsons, of which we shall 

 avail ourselves. " The compound eye of the com- 

 mon or grey dragon fly" (Libdlula Vulgata), says 

 Mr. Parsons 'Swhen examined externally, may be 

 divided into two parts ; one superior and posterior, 

 of an obscure red colour, and provided with facets 



* Encycl. Metropol., Art. LIGHT. 

 f Act, Cur, Bonn ; and Meikel's Archiv. 1829. 



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