198 THE ENTOMOLOGIST. 



anterior crossing those from the posterior, before they enter 

 the optic ganglia. Miiller, in his classical work on the 

 organs of sense, pointed out the fact that the eyes of Arthro- 

 pods, which are adapted for seeing in the water, do not differ, 

 in the distance of the recipient structures from the cornea, 

 or in the relative convexity of the latter, from those which 

 are adapted for vision in air, as they should if dioptric vision 

 existed. 



INTKODUCTORY PAPERS ON LEPTDOPTERA. 



By W. F. KiRBY, 



Assist. -Naturalist in the Museum, Eoyal Dublin Society. 



No. III. NYMPHALIDiE— DANAIN^. 



The classification of Lepidopiera is confessedly exceed- 

 ingly difficult, and is still far from satisfactory. Many 

 groups are natural, and are recognized as such at a glance ; 

 but it is extremely difficult to determine the relations in 

 which these stand to one another, and our existing arrange- 

 ments can only be regarded as tentative. It would there- 

 fore be out of place to discuss the various systems in detail 

 in a series of elementary papers, and 1 will only briefly 

 mention those of the butterflies here. 



Linne commenced his classification of Lepidopiera by 

 arranging the largest and handsomest species at the head of 

 each genus, without much regard to structure, and he con- 

 sequently placed the swallow-tails and the great blue South 

 American butterflies {Morpho, &c.) in the same group, at the 

 head of his genus Papilio, although the former have six 

 perfect legs, and the front pair of the latter are atrophied. 

 His successors removed these species, but both Boisduval and 

 Doubleday left the six-legged swallow-tails, forming their 

 restricted genus, Papilio, at the head of the butterflies. 

 More recently, however, Bates has re-arranged the families of 

 butterflies according to a system adopted by several con- 

 tinental entomologists since the time of Linne, placing those 

 families of butterflies in which the front legs are least deve- 

 loped at the head, and those which have six perfect legs next 

 to the moths; and his system, being recognized as the most 

 natural, is now generally adopted by English and German 



