268 E. J. SPITTA ON THE COMPOUND EYES OF INSECTS. 



Indeed, any of these causes — taken together or separately — might 

 cause the convexity of the centre, and give rise to the lens -like 

 front of which we have spoken. Then, again, the effect may 

 be purely optical, for the appearance of the little holes in the 

 artificial cornea strongly reminds one of that presented by the 

 real facets, and there can be nothing like a round front in 

 the photograph of the perforated zinc. 



Although it does not bear directly on the multiple-image 

 effect of the compound eye of the insect, still it might be taken 

 in the light of something akin to an omission if no reference 

 were made to Exner's experiment, as related by Carpenter. 

 He produced a photograph of a window of his apartment 

 through the eye of a Lampris, a result which attracted a good 

 deal of attention at the time. The retina and pigment were 

 removed, and the cornea and what remained of the eye were 

 filled with glycerine and water of a refractive index of 1'346. 

 It seems, however, to have escaped the attention of this illustrious 

 observer, that by this process he practically converted that which 

 remained of the eye into a lens with a refractive index of 

 1*346, which, of course, with the aid of the microscope, pro- 

 duced a photograph of the window of the apartment, just as 

 my artificial cornea did when an auxiliary lens was used to 

 take the place of the g^cerine one. In fact it may be said 

 that the photograph was obtained in spite of the cornea being 

 present. In the last edition of Dr. Packman's book, although 

 the name of Exner is frequently mentioned, no account of this 

 experiment appears to be given. It would seem that such omission 

 can only be by mutual consent. 



Jowrn. Quekett Microscopical Club, Scr. ?, Vol. IX., No. 58, April 1906 



