Page:Geology and Mineralogy considered with reference to Natural Theology, 1837, volume 1.djvu/304

 300 of vision, through which the light of heaven was admitted to the sensorium of some of the first created inhabitants of our planet.

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 marvellous facts yet disclosed by geological researches; and the structure of these eyes supplies an argument, of high importance in connecting together the extreme points of the animal creation. An identity of mechanical arrangements, adapted to the construction of an optical instrument, precisely similar to that which forms the eyes of existing insects and Crustaceans, affords an example of agreement that seems utterly inexplicable without reference to the exercise of one and the same Intelligent Creative power.

Professor Müller and Mr. Straus have ably and amply illustrated the arrangements, by which the eyes of Insects and Crustaceans 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 Butter-fly, to the number of 35,000 facets in the two eyes, and in the Dragon-fly to 14,000.

It appears that 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 principles of construction, we find both in their form, and in