vn 



far gone down that its rays only touch the visible part of the earth more or 

 less horizontally and are consequently still more tempered by trees and unevenesses 

 of the ground, something sets in which compared with the blazing day-light 

 we may call a kind of twilight lasting from a quarter of an hour to as much 

 as half an hour. Something similar happens in the morning. The Rhopalocera, 

 however, that fly then belong only to a few species, as is also the case with 

 those that live continually in the twilight of the dense forests or in the heavy 

 clouded mountains; their number is insignificant compared with the others 

 which are real Diunia and even, for a great part, true children of the sun. 



Conversely the same thing happens in the Heterocera. Comparatively many 

 species of this group fly by day and even in full sunshine, but still their 

 number is insignificant, compared with the multitude of real Nocturna. 



After thus choosing a somewhat broader biological point of view, more in 

 keeping with nature than systematism pure and simple, one has still a right 

 to make a general distinction between the aforesaid two large groups : the 

 Diurna and the Nocturna. 



The more so as all Lepidoptera belonging to each of these groups are 

 evidently adapted to that difference in mode of life, so much so that some of 

 the organs connected with this have either assumed a special form, or on 

 becoming useless have been atrophied. The latter happened, as far as the 

 Rhopalocera are concerned with regard to the frenulum already spoken of, 

 the former especially with regard to the form of the antennae. For why this 

 form differs so much in the two groups is, indeed, not known to us, but that 

 such a difference exists and is even rather considerable, cannot be denied; that 

 the cause of this lies in the difference of the mode of life is, it is true, a supposition, 

 but one to which we may surely attach some importance for this further reason 

 also that the antennae are undoubtedly organs adapted to sense perception. 



The thread-like, yet stiff club-shaped antennae, which characterize the 

 Rhopalocera, are found in them just as normally as the frenulum in the 

 Heterocera. And this is the case with all Lepidoptera, belonging to each of 

 these groups ; such Rhopalocera as perform their functions of life in the 

 twilight, have the same antennae as the others, just as well as those Heterocera 

 which fly in the sunshine agree with the other moths, both as regards the 

 form of the antennae and the presence of the frenulum. Hence there cannot be 

 much doubt that such species as have become somewhat differentiated in their 

 mode of life from the great body of their group, though now in that respect 

 approaching the other group, yet originally followed the habits of the group 

 with which they still agree in structure of body, and only became differentiated 

 from them at a later date. If we ask ourselves then to which of the two groups 



