Hudson. — N .Z. Insects illustrating Principle of Sexual Selection. 433 



Homoptera (cicadas), Darwin remarks that " throughout the animal king- 

 dom we often find the same object gained by the most diversified means ; 

 this seems due to the whole organization having undergone multifarious 

 changes in the course of ages, and as part after jjart varied different 

 variations were taken advantage of for the same general purpose. The 

 diversity of means for producing sovmd in the three families of Orthoptera 

 and in the Homoptera impresses the mind with the high importance of 

 these structures to the males, for the sake of calling or alluring the 

 females. We need feel no surprise at the amount of modification which 

 the Orthoptera have undergone in this respect, as we now know, from 

 Dr. Scudder's remarkable discovery, that there has been more than ample 

 time. This naturalist has lately found a fossil insect in the Devonian 

 formation of New Brunswick, which is furnished with ' the well-known 

 tympanum or stridulating-apparatus of the male Locustidae.' The insect, 

 though in most respects related to the Neuroptera, appears, as is so often 

 the case with very ancient forms, to connect the two related Orders of the 

 Neuroptera and Orthoptera."* 



The males of the walking-stick insects, or Phasmidae, are extremely 

 attenuated creatures, whilst the females are much stouter and larger, and 

 exhibit such great structural difierences that, in the absence of exact 

 knowledge to the contrary, they might easily be referred to a different 

 species, or even genus. In both sexes the appearance of the insect is most 

 perfectly adapted for concealment amongst vegetation, and the extra- 

 ordinary disparity between the sexes in this case is very difficult to explain. 



3. Order Neuroptera. 



In the order Neuroptera, which includes the termites, stone-flies, may- 

 flies, dragon-flies, caddis-flies, &c., there is little direct evidence of the 

 operation of sexual selection. In one of our largest may-flies, Ichtkyhotus 

 hudsoni, the male has two caudal setae which are very much longer than 

 the three possessed by the female. It is difficult to say, however, which 

 sex is the more ornamented. Of much greater interest for the purposes of 

 this paper are the nuptial dances in which the may-flies engage, and which 

 must often arrest the attention of those who are not entomologists. This 

 flight takes place shortly before sunset, and during its performance the 

 may-flies rise and fall in the air almost in perpendicular lines, and it is at 

 this time that pairing takes place. Of these remarkable dances Dr. Sharp 

 remarks that to the may-flies themselves the movements may, by the 

 number of the separate eyes, by their curved surfaces, and by the innumer- 

 able facets composing them, be multiplied and correlated in a manner of 

 which our own sense of sight allows us to form no conception. We can 

 see on a summer's evening how beautifully and gracefully a crowd of may- 

 flies dance, and ye may well believe that to the marvellous ocular organs 

 of the flies themselves these movements form a veritable ballet-dance. 



Amongst our small slender-bodied dragon-flies (Agrionina), often known 

 as " demoiselles," the males of Xanthagrion zealandicum have crimson 

 bodies, the females being dull bronze ; and in Lestes colensonis the body of 

 the male is marked with much more vivid blue than that of the female. 

 In the tribe Cordulina it is noteworthy that the male of Somatochlora 

 smithii has a brilliant metallic-green head, legs, and thorax, the same parts 

 in the female being much duller. 



* Descent of Man, 2nd ed., pp. 288-89, 1890. 



