40 HUMBLE CREATURES. 



external field, there can be little doubt that the 

 various images meet at a common centre, and are 

 conveyed to the brain as a single picture of the sur- 

 roimding field. We have only to consider the opera- 

 tion of our own eyes, to find a perfect illustration of 

 this principle ; for, although we look at one object 

 with both eyes, and consequently a distinct image is 

 refiected upon the retina of each, we do not see two 

 objects, but only one distinct image is apparent to 

 our sense. A still more remarkable example of the 

 fusion of images is, however, found in the action of 

 the stereoscope, where we actually have two objects, 

 or pictures, the images of which first pass through 

 two distinct lenses, and into our two eyes, and still 

 only one clear and prominent figure is carried to the 

 brain. 



You will perhaps inquire why such pains have 

 been taken to provide the Fly and other insects with 

 so many hundreds of eyes, whilst we and the higher 

 animals are furnished only with two of these organs. 

 Many explanatory replies have been given to this 

 question, few, however, being at all satisfactory; and 

 experiments have of late been tried in connexion 

 with the function of the simple and compound eyes 

 (the former of which are composed of similar parts to 

 the single facets of the latter), whereby we should be 

 led to the belief that the two sets of eyes do not 

 operate alike ; namely, that the one set reflects distant 

 objects, whilst the other enables the creature to 

 examine those in its immediate vicinity. Further 



