III.] INDEPENDENT SIMILARITIES OF STRUCTURE. 87 



tain comparative rapidity of development. Finally, and 

 this is perhaps one of the most curious circumstances, the 

 process of formation appears to have been, at least in some 

 respects, the same in the eyes of these molluscous animals 

 as in the eyes of vertebrates. For in these latter the cornea 

 is at first perforated, while different degrees of perforation 

 of the same part are presented by different adult cuttle- 

 fishes large in the calamaries, smaller in the octopods, 

 and reduced to a minute foramen in the true cuttle-fish 

 sepia. 



Some may be disposed to object that the conditions 

 requisite for affecting vision are so rigid that similar results 

 in all cases must be independently arrived at. But to this 

 objection it may well be replied that Nature herself has 

 demonstrated that there is no such necessity as to the 

 details of the process. For in the higher Annulosa, 

 such as the dragon-fly, we meet with an eye of an 

 unquestionably very high degree of efficiency, but formed 

 on a type of structure only remotely comparable with 

 that of the fish or the cephalopod. The last-named 

 animal might have had an eye as efficient as that of 

 a vertebrate, but formed on a distinct type, instead of 

 being another edition, as it were, of the very same 

 structure. 



In the beginning of this chapter examples have been 

 given of the very diverse mode in which similar results 

 have in many instances been arrived at; on the other hand, 

 we have in the fish and the cephalopod not only the eye, 

 but at one and the same time the ear also similarly evolved, 

 yet with complete independence. 



Thus it is here contended that the similar and complex 

 structures of both the highest organs of sense, as developed 



