38 Riley Presidential Address. 



and experiment, arid draw conclusions from well attested results. 



SIGHT. Taking first the sense of sight, much has been written 

 as to the picture which the compound eye of insects produces 

 upon the brain or upon the nerve centers. Most insects which 

 undergo complete metamorphoses possess in their adolescent states 

 simple eyes or ocelli, and sometimes groups of them of varying size 

 and in varying situations. It is difficult, if not impossible, to 

 demonstrate experimentally their efficiency as organs of sight ; 

 the probabilities are that they give but the faintest impressions, 

 but otherwise act as do our own. The fact that they are pos 

 sessed only by larva? which are exposed more or less fully to the 

 light, while those larva? which are endophytous, or otherwise hid 

 den from light, generally lack them, is in itself proof that they 

 perform the ordinary functions of sight, however low in degree. 

 In the imago state the great majority of insects have their simple 

 eyes in addition to the compound eyes. In many cases, however, 

 the former are more or less covered with vestiture, which is an 

 other evidence that their function is of a low order, and lends 

 weight to the view that they are useful chiefly for near vision 

 and in dark places. The compound eyes are prominent and ad 

 justable in proportion as they are of service to the species, as wit 

 ness those of the common House-fly and of the Libellulida? or 

 Dragon-flies. It is obvious from the structure of these com 

 pound eyes that impressions through them must be very differ 

 ent from those received through our own, and, in point of fact, 

 the late experimental researches of Hickson, Plateau, Tocke and 

 Lemmermann, Pankrath, Exner and Viallanes, practically estab 

 lish the fact that while insects are short-sighted and perceive 

 stationary objects imperfectly, yet their compound eyes are better 

 fitted than the vertebrate eye for apprehending objects set in re 

 lief or in motion, and are likewise keenly sensitive to color. 



So far as experiments have gone, they show that insects have 

 a keen color sense, though here again their sensations of color 

 are different from those produced upon us. Thus, as Lubbock 

 has shown, ants are very sensitive to the ultra violet rays of the 

 spectrum, which we cannot perceive, though he was led to con 

 clude that to the ant the general aspect of nature is presented in 

 an aspect very different from that in which it appears to us. In 

 reference to bees, the experiments of the same author prove 

 clearly that they have this sense of color highly developed, as 



