Remarks on the Trilohite. 29 



ceased to live many thousands, and perhaps miUions of years ago. 

 We must regard these organs with feehngs of no ordinary kind, 

 when we recollect that we have before us the identical instru- 

 ments of vision, through which the light of heaven was admitted 



to the sensorium of some of tlfc first created inhabitants of our 

 planets. 



" The discovery of such instruments in so perfect a state of 

 preservation, after having been buried for incalculable ages in the 

 early strata of the transition formation, is one of the most marvel- 

 lous facts yet disclosed by geological researches ; and the struc- 

 ture of these eyes supplies an argument, of high importance in 

 coiuiecting together the extreme points of the animal creation. 

 An identity of mechanical arrangements, adapted to the construc- 

 tion of an optical instrument, precisely similar to that which 

 forms the eyes of existing insects and crustaceans, affords an ex- 

 ample of agreement that seems utterly inexplicable without refer- 

 ence to the exercise of one and the same Intelligent Creative 

 Power. 



^^ Professor Miiller and Mr. Straus have ably and amply illus- 

 trated the arrangements, by which the eyes of insects and crusta- 

 ceans are adapted to produce distinct vision, through the medium 

 of a number of minute facets, or lenses, placed at the extremity 

 of an equal number of conical tubes, or microscopes ; these 

 amount sometimes, as in the butterfly, to the number of 35,000 

 fa-cets in the two eyes, and in the dragon-fly to 14,000. 



" It appears tliat in eyes constructed on this principle, the image 

 will be more distinct in proportion as the cones in a given portion 

 of the eye are more numerous and long ; that, as compound eyes 

 see only those objects which present themselves in the axes of the 

 individual cones, the limit of their field of vision is greater or 

 smaller as the exterior of the eye is more or less hemispherical. 



" If we examine the eyes of trilobites with a view to their prin- 

 ciples of constniction, we find both in their form, and in the dis- 

 position of the facets, obvious examples of optical adaptation. 



" In the asaphus caudatus each eye contains at least 400 nearly 

 spherical lenses fixed in separate compartments on the surface of 

 the cornea. The form of the general cornea is peculiarly adapted 

 to the uses of an animal destined to live at the bottom of the wa-^ 

 ter : to look downwards was as much impossible as it was unne- 

 cessary to a creature living at the bottom ; but for horizontal vis- 



