228 ORGAN'S OF EXTEEME PEKFECTION. [Chap. VI. 



highest human intellects ; and we naturally infer that 

 the eye has been formed by a somewhat analogous 

 process. But may not this inference be presumptuous ? 

 Have we any right to assume that the Creator works by 

 intellectual powers like those of man ? If we must 

 compare the eye to an optical instrument, we ought in 

 imagination to take a thick layer of transparent tissue, 

 with spaces filled with fluid, and with a nerve sensi- 

 tive to light beneath, and then suppose every part 

 of this layer to be continually changing slowly in 

 density, so as to separate into layers of different densities 

 and thicknesses, placed at different distances from each 

 other, and with the surfaces of each layer slowly changing 

 in form. Further we must suppose that there is a 

 power, represented by natural selection or the survival 

 of the fittest, always intently watching each slight 

 alteration in the transparent layers; and carefully 

 preserving each which, under varied circumstances, in 

 any way or in any degree, tends to produce 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 destroyed. In living bodies, variation 

 will cause the slight alterations, generation will 

 multiply them almost infinitely, and natural selection 

 will pick out with 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 thus be formed as superior to one of glass, as the 

 works of the Creator are to those of man ? 



