THE CRUST OF THE EARTH. 



Annelida, with which their remains are found associated. But 

 one of the most interesting facts connected with them is the 

 structure of their eyes, which resemble those of insects described 

 in our Tract on " Microscopic Drawing." They consist of a vast 

 number of minute lenses of octagonal form, set in the ends of 

 tubes arranged side by si^e, so as to produce a radiating mass of 

 eyes, enabling the animal to look at the same time in every direc- 

 tion. As many as four hundred of these lenses have been found 

 set in a single cornea. 



63. Such a structure proves, if proof were wanted, that the 

 properties of light, and of the transparent media constituting the 

 atmosphere and water, were, at the remote epochs when the earth 

 was tenanted by those creatures, what they now are. " With 

 respect to the waters," says Dr. Buckland, in reference to these 

 creatures, "we conclude that they must have been pure and 

 transparent enough to allow the passage of light to organs of 

 vision, the nature of which is so fully disclosed by the state of 

 perfection in which they are preserved. With regard to the 

 atmosphere, also, we infer, that had it differed materially from 

 its actual condition, it might have so far affected the rays of light 

 that a corresponding difference from the eyes of existing Crus- 

 taceans would have been found in the organs on which the 

 impressions of such rays were then received, Regarding light 

 itself, also, we learn, from the resemblance of these most ancient 

 organisations to existing eyes, that the mutual relations of light 

 to the eye, and of the eye to light, were the same at the time 

 when Crustaceans, endowed with the faculty of vision, were first 

 placed at the bottom of the primeval seas, as at the present 

 moment. Thus we find among the earliest organic remains, an 

 optical instrument of most curious construction, adapted to 

 produce vision of a peculiar kind, in the then existing repre- 

 sentatives of one great class in the articulated division of the 

 animal kingdom. We do not find this instrument passing onwards, 

 as it were, through a series of experimental changes, from the 

 more simple into more complex forms : it was created, at the very 

 first, in the fulness of perfect adaptation to the use and condition 

 of the class of creatures to which this kind of eye has ever been, 

 and is still, appropriate. If we should discover a microscope, or 

 telescope, in the hand of an Egyptian mummy, or beneath the 

 ruins of Herculaneum, it would be impossible to deny that a 

 knowledge of the principle of optics existed in the mind by which 

 such an instrument had been contrived. The same inference 

 follows, but with cumulative force, when we see nearly four 

 hundred microscopic lenses set side by side in the compound eye 

 of a fossil trilobite ; and the weight of the argument is multiplied 

 60 



