EYES 



985 



which the student must be referred for complete information. 1 The 

 kind of image formed by the compound eye lias long been a matter 

 of discussion amongst physiologists. 2 



The process of taking the photo-micrograph copied in fig. 734 

 was this : The eye of the Lampyris was carefully dissected out from 

 the head, the retina and pigment removed with a fine camel-hair 

 pencil, and the back of the eye immersed in a mixture of glycerin 

 and water, possessing a refractive index of 1 "346 ; this was already 

 known to be the refractive index of the blood of the Lampyris. The 

 whole was placed upon an ordinary cover-glass, this being fixed by 

 its edges to a slide or object-carrier with a circular aperture cut in 

 it, as in fig. 735, C ; a is the slide with an aperture less in diameter 



I) 



C 



FIG. 735. Diagrammatic illustration of the method by which 

 the image in fig. 734 was photo-micrographed. 



than the cover-glass b cut through it; c is the fluid-medium of 

 ^=1-346 in which the back parts of the eye are immersed, thus 

 fulfilling the conditions of living sight, while the cornea with its 

 lenses is shown at d, being, as in the normal state, in air. If the eye 



1 Sitzungsber. ATtad. Wissensch. Wien, Bd. xcviii. (1889), pp. 13, 143 ; also Die 

 Pliysiologie der facettirten Augen von Krebsen und Insecten (Leipzig und Wien, 

 1891). 



2 A critical history of the discussion will be found in Chapter VII. of Sir J. 

 Lubbock's Senses of Animals (London, 1888), and in Dr. D. Sharp's Annual Address 

 to the Entomological Society of London, 1888 (1889). See also Mr. A. Mallock in Proc. 

 Boy. Soc. Lond. vol. Iv. p. 85. The question of the physiology of the compound eye 

 of Arthropods has given rise to much discussion. For further details as to its 

 structure consult Grenadier's great work, Untersuchungen uber das Sehorgan der 

 Artliropoden &c. (Gb'ttingen, 1879) ; Carriere, Die Sehorgane der Thiere &c. (Munich 

 and Leipzig, 1885) ; Hickson, ' The Eye and Optic Tract of Insects,' Quart. Journ. 

 Microsc. Sci. xxv. p. 215; Lankester and Bourne, 'The Minute Structure of the 

 Lateral and Central Eyes of Scorpio and Limulus,' Quart. Journ. Microsc. Sci. 

 xxiii. p. 177 ; Lowne, ' On the Compound Vision and the Morphology of the Eye in 

 Insects,' Trans. Linn. Soc. (2), ii. p. 389 ; Patten, ' Eyes of Molluscs and Arthropods,' 

 Mitth. Zool. Stat. Neapel, vi. 



