300 COMPOUND AND FACETTED. 



struments of vision, through which the light of heaven M'as 

 admitted to the sensorium of some of the first created inha- 

 bitants 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 re- 

 searches ; and the structure of these eyes supplies an argu- 

 ment, 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 in- 

 strument, precisely similar to that which forms the eyes of 

 existing insects and Crustaceans, affords an example of 

 agreement that seems utterly inexpUcable without reference 

 to the exercise of one and the same Intelligent Creative 

 power. 



Professor Miiller 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 them- 

 selves in the axes of the individual cones, the hmit 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 



* See Lib. Ent Knowledge, v. 12. ; and Dr. Rogel's Bridgewatcr Trea- 

 tise, vol, ii. p. 486 ct seq. and Fig. 422 — 42S. 



