64 THE GENESIS OF SPECIES. [CnAi-. 



that those steps were never i:)ro{luced by " Natural Selec- 

 tion." 



The eye is formed by a simultaneous and corresponding" 

 ingrowth of one part and outgrowth of another. The skin 

 in front of the future eye becomes depressed, the depres- 

 sion increases and assumes the form of a sac, ^vhich 

 changes into tlie aqueous humor and lens. An outgrowth 

 of brain-substance, on the other hand, forms the retina, 

 while a third process is a lateral ingrowth of connective 

 tissue, which afterward changes into the vitreous humor of 

 the eye. 



The internal ear is formed by an involution of the in- 

 tegument, and not by an outgrowth of the brain. But tis- 

 sue, in connection with it, becomes in part changed, thus 

 forming the auditory nerve, whicli places the tegumentary 

 sac in direct communication with the brain itself. 



Now, these complex and simultaneous coordinations 

 could never have been produced by infniitesimal begin- 

 nings, since, until so far developed as to efl'ect the requi- 

 site junctions, they are useless. But the eye and ear when 

 fully developed present conditions which are hopelessly dif- 

 ficult to reconcile with the mere action of " Natural Selec- 

 tion." The dilhculties witli regard to the eye had ])een 

 well put by Mr. ]\Iur])Iiy, especially that of the concordant 

 result of visual development springing from diiferent start- 

 ing-points and continued on by independent roads. 



He says,^' speaking of the beautiful structure of the 

 perfect eye, " The higher the organization, whether of an 

 entire organism or of a single organ, the greater is the 

 number of the parts that cooperate, and the more perfect 

 is their cooperation ; and consequently, the more necessity 

 there is for corresj)oiHling variations to take j)lace in all the 

 cooperating parts at once, and the more useless will be any 

 variation whatever unless it is accompanied by corresjioud- 



«^ *' Habit and Intelligence," vol. i., p. 319. 



