300 PROCEEDINGS OP THE ACADEMY OF [1884. 



HOMOLOGIES OF THE VERTEBRATE CRYSTALLINE LENS, i 

 BY BENJAMIN SHARP, M. D., PH. D. 



I cannot better introduce my subject than by quoting the 

 following passage from Chas. Darwin : " To suppose that the 

 eye, with all its inimitable contrivances for adjusting the focus 

 to different distances, for admitting different amounts of light, 

 and for the correction of spherical and chromatic aberration, 

 could have been formed by natural selection seems, I freely 

 confess, absurd in the highest possible degree. Yet reason tells 

 me that, if numerous gradations from a perfect and complex eye 

 to one very imperfect and simple, each grade being useful to its 

 possessor, can be shown to exist ; if, further, the eye does vary 

 ever so slightly, and the variations be inherited, which is certainly 

 the case ; and, if any variation or modification in the organ be 

 ever useful to an animal under changing conditions of life, then 

 the difficulty of believing that a perfect and complex eye could 

 be formed by natural selection, though insuperable b}' our 

 imagination, can be hardly considered real. How a nerve comes 

 to be sensitive to light, hardly concerns us more than how life 

 itself first originated ; but I ma}^ remark that several facts make 

 me suspect that any sensitive nerve may be rendered sensitive to 

 light, and likewise to those coarser vibrations of the air which 

 produce sound. . . ."^ 



" If it could be demonstrated that any complex organ existed 

 which could not possibly have been formed by numerous, succes- 

 sive, slight modifications, my theory would absolutely break 

 down. But I can find out no such case. No doubt many organs 

 exist of which we do not know the transitional grades, more 

 especially if we look to much-isolated species, round which, 

 according to my theory, there has been much extinction. . . ."^ 



" In the cases in which we know of no intermediate or transi- 

 tional states, we should be very cautious in concluding that none 



' Being the principal part of an address delivered before the Biological 

 Section of the Academy of Natural Sciences of Philadelphia, December 

 15, 1884. 



''Darwin, Chas., "On the Origin of Species, by Means of Natural 

 Selection, etc." New lork (Appleton), 1861, p. 167. 



^ Darwin, Chas., Orig. of Species, etc., p. 169. 



