28 LtTCANlD^ ANt) PASSALIDiE, 



absence of any evidence of choice exercised by female insects 

 and the very doubtful existence of the aesthetic sense required 

 for an appreciation of the comparative attractions of their 

 suitors, a comparison of the eyes of the Lucanid^ with those 

 of other insects must soon convince us that their jjowers of 

 vision are quite inadequate for any such appreciation. The 

 compound eyes of insects consist of numerous elements, 

 each with a separate lens and external facet, which receive 

 the light from a small part of the field of vision, the result 

 being a mosaic jjicture, the clearness of which varies according 

 to the number of comj)onent lenses in the eye. In some 

 M^ell-cndowed insects, such as butterflies, these may be from 

 12,000-20,000 in a hemisphere on each side of the head, so 

 that the light is collected from every jjossible direction. The 

 two hemisj)heres may occupy most of the head, as in some 

 Dragonflies, which may have as many as 28,000 facets in 

 each eye. 8ome beetles, such as the Tiger-beetles (Cicin])E- 

 iadje), wliich are very agile and pre}' u2Jon other insects, 

 also have large prominent eyes witli many facets, but most 

 have rather poor sight and the 8tag- beetles are amongst 

 these. Li most the eyes are very small and consist of a few 

 hundred facets only. In Lucanus cerviis there are about 

 2,000 and in most Lucanid^ less than that. The eyes are 

 far apart and so placed that no comprehensive outlook is 

 possible. In some of the great sj^ecies, like those comijosuig 

 the genus Calcodes, each eye is comi^letely divided into two 

 halves, the larger placed beneath the head for the perception 

 of objects lymg between the fore-legs, while the other half 

 is level with the upper surface of the head and can receive 

 intimations only of conditions immediately above. There is 

 even a -species of Lucanid^, Vinsonella cwca, in the island of 

 Mauritius which, although sexually dimorphic hke most of 

 the family, is totally' blind. In Aulacostethus archeri, Plate 

 XXI, figs. 7 and 8, the eyes are so greatly reduced that the 

 sight must be Cixtremely feeble, and in others they can be of 

 very little use. Even insects, such as butterflies, with com- 

 paratively good sight are easily deceived by artificial flowers 

 or coloured imitations and only convinced of their error after 

 repeated antl close investigations. 



The fact is that in uisects many of the fimctions served by 

 the eyes in higher animals are performed by the antenna.', 

 the seat of the olfiictory sense, which is nnich more important 

 to them than that of sight and is develo])ed to greater perfection. 

 It is b}' that sense that insects are able to recognize other 

 individuals of theii- species as well as the substances wliich 

 serve them I'oi' food. The subordinate function of the eyes 

 is shown l)y tlie complicated operations often performed in 

 complete darkness by insects such as ants and bees, the 

 construction of the comb and feeding and tending of the 



