492 THE SENSORIAL FUNCTIONS. 



pound ; both of which are generally possessed by 

 the higher orders of winged insects. From the 

 circumstance that the compound eyes are not 

 developed before the insect acquires the power 

 of flight, it has been inferred that they are more 

 particularly adapted to the vision of distant ob- 

 jects ; but it must be confessed that the expe- 

 riments made on this subject have not, hitherto, 

 led to any conclusive results. Dug^s found, in 

 his trials, that after the stemmata had been 

 covered, vision remained apparently as perfect 

 as before ; whiJe, on the other hand, when in- 

 sects were deprived of the use of the compound 

 eyes, and saw only with the stemmata, they 

 seemed to be capable of distinguishing nothing 

 but the mere presence or absence of light. 

 Others have reported, that if the stemmata be 

 covered with an opaque varnish, the insect loses 

 the power of guiding its flight, and strikes 

 against walls or other obstacles ; whereas if the: 

 compound eyes be covered while the stemmata 

 remain free, the insect generally flies away, 

 rising perpendicularly in the air, and continuing 

 its vertical ascent as long as it can be followed 

 by the observer. If all the eyes of an insect 

 be covered, it will seldom make any attempt 

 whatsoever to fly. 



The eyes of insects, whether simple or com- 

 pound, are immoveably fixed in their situations ; 

 but the compound eyes of the higher orders of 



