THE SENSES OF INSECTS. 25 



insects both with and without ocelli, in addition to the com- 

 pound eyes, and with the same results. 



From repeated experiments on flies, bees, etc., butterflies 

 and moths, dragon-flies and beetles, Plateau concludes that 

 insects with compound eyes do not notice differences in 

 form of openings in a half-darkened room, but fly with 

 equal readiness to the apparently easy and apparently diffi- 

 cult way of escape; that they are attracted to the more 

 intensely lightened opening, or to one with apparently 

 greater surface; hence he concludes that they cannot dis- 

 tinguish the form of objects, at least only to a very slight 

 extent, though they readily perceive objects in motion. 



It is well known that honey-bees on leaving their hives 

 fly about as if making out the form of objects near their 

 home, and, after thus taking in the landmarks, can after a 

 few flights make a bee-line from a distance to their hives. 

 While this would seem opposed to the result of Plateau's 

 experiments, it may be said that a very near-sighted man 

 can find his way home; objects even perceived very indis- 

 tinctly serving to guide him. Insects also without doubt 

 distinguish the difference in color of objects; it is well known 

 that butterflies will descend from a position high in the air, 

 mistaking white bits of paper for white flowers; while, as 

 we have observed, white butterflies (Pieris) prefer white 

 flowers, and yellow butterflies (Colias) appear to alight on 

 yellow flowers in preference to white ones. 



Until further experiments are made, it seems probable, 

 then, that all insects do not have acute sight, that they see 

 objects best when moving, and on the whole except dragon- 

 flies and other predaceous, swiftly flying insects, such as 

 certain flies, wasps and bees, which have very large rounded 

 eyes insects are guided mainly rather by the sense of smell 

 than that of sight. 



Some insects can only detect light from darkness; while, 

 to go to the other extreme, a few may see " with clearness 

 and precision, by means of inverted images, either a land- 

 scape or small neighboring objects." We may add with 



