^^"" ZOOGENESIS ^^^^ 



really exist in darkness more or less complete, for all 

 is dim twilight within the outer body covering. 



From its original function as a protection against 

 an excess of light, coloration has secondarily been 

 developed toward the end of making sunlight useful 

 through the formation of endless varied and often 

 complicated color patterns by which the eyes of 

 enemies are more or less deceived. 



Animals with bodies adequately protected against 

 harm from sunlight find sunlight extremely useful in 

 enabling them to find their food and to avoid their 

 enemies. This they do by means of eyes. 



Every land creature living in the open, no matter 

 what it is, possesses eyes which, though they vary 

 greatly in perfection, are always adequate for the 

 needs of each. Even nocturnal creatures possess eyes, 

 most of them good eyes and some extraordinary eyes, 

 though a few have eyes which are only serviceable in 

 distinguishing night from day. 



Taken collectively, eyes serve three different pur- 

 poses. They may be, as with us, organs of vision 

 giving a continuous photographic record of the sur- 

 roundings. This is the usual type of eye found in the 

 creatures of the land, as in all the vertebrates and in 

 practically all insects in the adult stage. Eyes may 

 simply be organs to record the varying intensity of 

 illumination and without a visual function, or at least 

 with a very limited visual capacity. Such are the 

 eyes of snails, slugs and caterpillars. Or eyes may 

 simply record the relative intensity of heat. In this 

 case they are usually represented by black spots more 



