26 



INSECTS. 



composed of many cylindrical, or rather conical eyes 

 (which for convenience sake we will call eyelets), whereas 

 the common idea of an eye is that it is an organ of 

 globular form. It would require more space than can 

 he afforded here to describe the structure of the cylin- 

 drical eyelet ; it must suffice to say that in it are repre- 

 sented nearly all the principal parts which exist in the 

 human eye, even to the iris and pupil, although together 

 they form a long slender cone instead of a globe* (fig. 2). 

 Fig. 2. This striking dif- 



ference finds its 

 explanation when 

 we consider that 

 this form, by re- 

 ducing the rays 

 of light which can 

 possibly reach the 

 retina to such 



only as fall di- 

 Eyes of Hive Bee (Male). rectly uponit} pre . 



vents the confusion which would arise from the recep- 

 tion by each eyelet of images from all sides. It may be 

 observed here that some insects (e.g. the butterfly) 

 possess as many as 34,650 of these eyelets. 



Very curious observations have been made upon the 

 connexion which exists between the size and position of 

 the eyes, and the flight of the insect. Thus the dragon- 

 flies and butterflies, alike remarkable for the freedom 

 and extent of their flight, have large and convex eyes, 

 so placed that the field of vision must be very great. 

 Others again, as the bees, which have long and narrow 



* In this figure (partly borrowed from Dr. Carpenter) the lenses are 

 made large out of proportion, in order the better to show their form. 



