CiiAr. VI. AND COMPLICATION. 181 



It is scarcely possible to avoid comparing tlic eye with a 

 telescope. We know tliat tliis instrument lias been peri'eeted 

 by the long-continued ell'orts of the highest human intellects ; 

 and we natm-ally infer that the eye has been formed by a some- 

 what analogous process. But may not this inference be pre- 

 sumptuous ? Have we any right to assume that the Creator 

 works by intellectual powers like those of man? If we must 

 compare the e^'e to an ojjtical instrument, we ought in imagi- 

 nation to take a thick layer of transparent tissue, with spaces 

 tilled with fluid, and with a nerve sensitive to light beneatlt, 

 and then suppose every ])art of this layer to be continually 

 changing slowly in d(Misity, so as to separate into layers of 

 dillerent densities and thicknesses, placed at different distances 

 from each other, and with the surfaces of each layer slowly 

 changing in form. Further, Ave must suppose that there is a 

 power, r(>presented by natural selection or the survival of the 

 Mttest, always intently watching each sliglit alteration in the 

 transparent la^'ers ; and carefully preserving eaoli which, undc^' 

 varied circumstances, in any way or in any degree, tends to 

 jiroduce a distincter image. We must suppose each new state 

 of the instrument to be multiplied by the million; each to be 

 preserved until a better one is produced, and then the old ones 

 to be all destroj-ed. In living bodies, variation will cause the 

 slight alterations, generation will multiply them almost infi- 

 nitely, and natural selection Avill pick out Avith unerring skill 

 each improvement. Let this process go on for millions of 

 years ; and during each year on millions of individuals of many 

 kinds; and may we not believe that a living optical instrument 

 might tluis be formed as superior to one of glass, as the works 

 of the Creator are to those of man ? 



Modes of Transition. 



If it could be demonstrated that any com])lex organ existed, 

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

 cessive, slight modifications, my theor}- would absolutely break 

 down. But I can find out no such case. No doubt manv or- 

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

 more especially if we look to much-isolated spt^cies, roimd 

 which, according to the theory, there has been nujch extinction. 

 Or again, if we take an organ common to all the members of 

 a large class, for in this latter case the organ must have been 

 originally fonnod at an extremely remote period, since which 



