Page:Divine Selection or The Survival of the Useful.djvu/65

 with, hair sacs. They are now metamorphosed hair sacs. The crystalline lens of the eye is also, we are told, a differentiated hair sac, and the aqueous and vitreous humor are liquefied, dermal tissue.

Says Mr. Fiske, in commenting upon this, "One can seem to discern how in the history of the eye there was at first a concentration of pigment grains in a particular dermal sac, making the spot exceptionally sensitive to light; then came by slow degrees the heightened translucence, the convexity of surface, the refracting humor and the multiplication of nerve vesicles arranging themselves as rectinal rods." In other words, the eye was formed by the impact of light rays upon pigment grains in a dermal sac. The ear is represented to have been formed in a like manner by adjustment of other dermal sacs to the sound wave.