^6 THE GENESIS OF SPECIES. [Chap. 



auditory organ in a very inferior condition ot" development 

 to what we find in the dibninch : tlms we have not only 

 evidence of the independent high develo])nient of the 

 orL,'an in the former, but also evidence pointing towards a 

 certain degree of comparative rapidity in its development. 



Such being the case with regard to the organ of hearing, 

 we have another yet stronger argument witli regard to the 

 organ of sight, as has been well pointed out by Mr. J. J. 

 ^Furpliv.^ He calls attention to the fact that the eye must 

 have been perfected in at least " three distinct lines of 

 descent," alluding not oidy to the molluscous division of 

 the animal kingdom, and the division provided with a 

 spinal column, Init also to a third i)rimary division, viz. 

 that which includes all insects, spiders, crabs, &c., which 

 are spoken of as Annulosa, and the type of whose structure 

 is as distinct from that of the molluscous type on the 

 one hand, as it is from that of the vertel)rate type on 

 the other. 



In the cuttle-fishes we find an eye constructed even 

 more completely on the vertebrate type than is the ear. 

 Sclerotic, retina, choroid, vitreous humour, lens, aqueous 

 humour, all are present. The correspondence is wonder- 

 fully com]»lete, and there can hardly be any hesitation in 

 saying that for such an exact, prolonged, and correlated 

 series of similar structures to have been brought about in 

 two independent instances by merely indefinite and minute 

 accidental variations, is an improbability w liich amounts 

 virtually to impossibility. Moreover, we have here again 

 tlie same imi)erfection of the four-gilled cei)halopod, as 

 compared with the two-gilled, and therefore (if the latter 

 proceeded from the former) a similar indication of a cer- 

 1 See "Habit and Intelligence," vol. i. j.. 321. 



