1870.] 285 [Burgeas. 



• 

 hare an independent motion, the whole apical apparatus, including 

 the hooks, having a common vertical movement upon the main body, 

 and the central tooth a forward and backward swing upon the apical 

 portion. 



Besides the asymmetry of the dorsal crest, to which we have re- 

 ferred, the lateral arms, the terminal hooks and the inferior armature, 

 (as will be seen in the hind view of the upper organ of N. tristis), 

 frequently partake of the same peculiarity; indeed, this element 

 seems to pervade every part of the remarkable genital armature in 

 this genus, as a study of the following descriptions and illustrations, 

 in which we pass from the simpler to the more complex form, will 

 show. 



One reason, doubtless, that this strange asymmetry has escaped 

 observation, is the entire concealment of the parts by scales, and the 

 want of attention to these appendages in butterflies; the upper organ 

 is protected by an extensive posterior expansion of the terminal 

 segment of the abdomen, which forms a projecting hood, and which 

 is also provided at tip with a heavy fringe of excessively long scales; 

 the clasps are themselves furnished externally with a heavy coating 

 of pretty long scales, which effectually hides the sculpture of the 

 parts; although the disparity in length of the two clasps is readily 

 seen, when it is so marked as in N. Brizo. 



In endeavoring to assign a reason for this excessive development 

 and remarkable asymmetry of the external genital organs, one can- 

 not but be struck by the fact that the males of this genus are far 

 more commonly met with than the females; whether this is due to 

 the comparative scarcity of the latter, or to the greater seclusion of 

 their haunts — all the species are sylvan — we are not prepared to say ; 

 the females, however, are taken in the same stations as the males, 

 and seem entirely at home there ; so that we are inclined to adopt the 

 former hypothesis and to believe that, notwithstanding the simplicity 

 of the external genital apparatus in the' female, the excessive devel- 

 opment of these parts in the male is in correlation with their superior 

 numbers, ensuring, beyond doubt, the impregnation of every female; 

 we do not, however, see how asymmetry gives any superior advan- 

 tage. It may be mentioned in this connection that when a male of 

 one of these species is taken between the fingers, the insect frequently 

 endeavors to use this apparatus as an organ of defence, or perhaps it 

 might be said, of aggression,. much after the manner of a Panorpa or 

 a Staphylinus. 



