VI 



separately differentiated from the Heterocera, show some more relics of them 

 still, so much so that the frenulum of the Heterocera, though very rarely, is 

 still found among them. It is true that systematism has, of late, dissociated 

 from the Hesperidae such species as those in which this organ is still present, 

 and classified them with the Heterocera (Castniidae) ; but this is only forcing 

 on one the rules of the system in contradiction with all natural affinity : for 

 these species also, according to their whole habitus, are real Hesperidae. And 

 as for the others, as Mr. Snellen assured me, we do not, indeed, find there 

 a fully developed brisde and loop, but still in the same place there are some 

 stiff hairs performing the same function, whose presence, as far as they are 

 concerned, seems to point to a very close affinity with the Heterocera. 



No doubt from the earliest times that people began to take some interest in 

 the once so much despised insects, they must have noticed that some Lepidoptera 

 fly chiefly by day, others in the dark, and that there is a structural difference 

 between the two classes. Indeed, in the vulgar tongue the two have always 

 borne different names, so that it is even very probable the conception that 

 they belong to the same group, is of a much later date, a conception which 

 forsooth even at the present day is almost absent among illiterate people. Hence 

 when science began to take notice of the Lepidoptera the above named distinction 

 — a biological one, since chiefly based on the animal's way of life — found 

 its expression in Latreille's division into Diiirna, Crepuscular ia, and Nodua. 

 Soon however, it became evident that the middle category was entirely factitious 

 and that the two others also were not quite correct, because many so-called 

 Nodua fly chiefly by day and even in a blazing sun ; afterwards it became 

 known also that many so-called Diunia do not chiefly fly by day, but in the 

 twilight. Then people tried to found a sytematic distinction on somatic characteristics 

 and so the two above named groups were accepted. But though we may agree 

 with this for the sake of an orderly arrangement in entomology, we should 

 not forget — however much systematism, especially in Germany, has aimed 

 at absolutism in this, and though its biological treatment has even been regarded 

 as not scientific — , that also the old division into Diunia and Nodua, at least 

 from a biological point of view contains much truth and that an impartial 

 naturalist ought to take this into account in his systematic arrangement as much 

 as possible. Looked at from this, in my opinion the correct, point of view, the 

 Hesperidae will continue to be classed among the Rhopalocera, I think. 



It is true that some Rhopalocera, in Java also, do not fly by day except 

 when roused, but only fly in the evening-twilight and probably also at dawn. 

 The twilight in the tropies does indeed not last very long, but still it is not so 

 short as astronomy teaches. For as soon as the sun in the evening has so 



