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XIV. On the Compound Vision and the Morphology of the Eye in Insects. By 

 B. Thompson Lowne, F.R.C.S., E.L.S., Lecturer on Physiology , Middlesex Hospital, 

 formerly Arris and Gale Lecturer, Royal College of Surgeons. 



(Plates XL.-XLIII.) 



Eead 7th February, 1884. 



J_HE manner in which the compound eye of arthropods subserves the function of 

 vision has been an undetermined problem since Johannes Midler enunciated his well- 

 known theory of mosaic vision in 1826 *. 



The views of naturalists on this subject, if we except the extremely improbable and 

 purely hypothetical view recently propounded by Exner f , may be grouped under two 

 heads : — some have supported Midler's hypothesis, or a modification of it % ; whilst others 

 have followed R. "Wagner, and held the view more commonly attributed to Gottsche §. 



It is well known that Midler supposed that each facet produces a single visual im- 

 pression and that the whole visual field consists of a mosaic of such impressions ; many 

 of his followers have modified this view, by supposing that a small number of visual impres- 

 sions are originated by each facet, the order of which is neither reversed nor inverted by 

 the dioptric apparatus. 



Midler's hypothesis was suggested to its learned author by the radial arrangement of 

 the parts of the compound eye about a hemispherical or nearly hemispherical retina, 

 and by the difficulty of conceiving a retina capable of correcting a mosaic of reversed 

 and inverted images, the order of which is neither reversed nor inverted. 



R. Wagner || was the first to throw doubt upon Midler's view : he mistook the capsule 

 of the crystalline cone for a retina, an error which was also committed by Ruete If and 

 Dor **. 



R. Wagner and his followers regard the compound eye as an aggregation of simple 

 eyes, the dioptric structures of each producing an image on a distinct retina, in the 

 same manner as the dioptric structures of the vertebrate eye, so that the whole visual 

 field is a mosaic qf reversed and inverted images, the order of which is neither reversed nor 

 in verted. 



The most important paper on this subject, after Midler's work, was undoubtedly a 

 short but well-known contribution to Midler's Archives by Gottsche in 1852. Leeuwen- 



* J. MiUler, ' Zur verglcichenden Physiol, des Gesichtssinnes des Menschen und der Thiere ' &e. 

 t Sigm. Exner. Biologisches CentraJblatt, Jahrg. i. p. 272, and Pop. Science Eeview, 1881, p. 337. 

 J Holmholtz, Du Bois Eeymond, J. Notthaft, &o. § Will. Zenker, &c. 



II Wiegniann's Archiv, 1835. Ed. i. p. 372. 



1" Gratulationsschrift der mod. Fac. zu Leipzig zu C. G. Cams 50-jahr. 1861. 

 ** Archiv d. Sciences Phys. et Natur. 1861. 

 SECOND SEKIES. — ZOOLOGY, VOL. II. 58 





