10 



AFRICAN MIMETIC BUTTERFLIES 



fore-wing. Except in the Lycaenidae, and some of the Pieridae, there is, close to the base, 

 a short, curved, and usually simple precostal nervure. In some genera this nervure is 

 forked, its lower branch being sometimes united to the costal, forming a minute prediscoidal 

 cell. Some discrepancy exists between the English and German methods of naming the 

 branches of the subcostal in the hind-wing, the second subcostal of English authors being 

 called the upper radial in Dr. Schatz's work. Thus the nervule marked udc in the figure 

 is regarded as the upper discocellular by the German nomenclature, and as the beginning of 

 the second subcostal according to the English system. The essential difference between 

 the two systems lies in the fact that while German naturalists count two radial nervules 

 in the hind-wing the English system recognizes only one. In the hind-wing of the genus 

 Hypolimnas and many others the discoidal cell is open as shown in the figure. The median 

 nervure has three branches as in the fore-wing, and in addition to the submedian nervure 

 there is the internal nervure which, though usually wanting or imperfectly developed in the 

 fore-wing, is well developed and independent in the hind-wing, except in the Papilionidae, 

 in which family it is absent. 



Another system occasionally used is that in which all the nervules and nervures reaching 

 the margin of the wing are numbered consecutively. In this system the posterior branch 

 of the median is always numbered 2, the nervures below this being all called i, and designated 

 when necessary la, ib, ic, so that the corresponding nervures in front and hind- wings bear 

 the same numbers. The nervures below the median are sometimes called branches of the 

 internal, and in the German nomenclature the internal is called the inner-margin nervure. 

 All these branches are sometimes called the anal nervures. 



The wings of butterflies are covered with scales, to the structure and pigmentation 

 of which their colours and patterns are due. These scales vary considerably in shape, but 

 are essentially flat chitinous structures which may contain colouring matter between their 

 upper and under surfaces, or the pigment may be intimately associated with the chitin. 

 In some cases, as in the metallic colours of the Morphinae, the colours are due, not to pig- 

 mentation, but to minute striations on the surface of the scale, the intervals of which being 

 shorter than certain of the wave lengths of light, cause what are known as interference 

 colours. Each scale is attached to the wing membrane by a stalk, and its outer edge overlaps 

 the points of attachment of the next scale. Many Lepidoptera have transparent wings, and 

 this transparency is brought about in a great variety of ways. In some cases the scales 

 are normal, but are devoid of pigment, in other cases they are set as it were on edge so that 

 the light passes between as through an open blind, or they may be reduced to mere hairs. 

 Certain moths emerge from the pupa with scaled wings, but the scales, owing to their feeble 

 attachment, all fall off in the first flight. The colouring matter of the scales, at least in the 

 Pieridae, has been shown by Professor Hopkins to be either uric acid or its derivatives, 

 and it is noteworthy in this connexion that Schaeffer has shown that each of the hypodermal 

 scale-forming cells contains an excretory vesicle. 



The compilation of a satisfactory classification of the group Rhopalocera is beset with 

 considerable difficulty, and various efforts in this direction have been productive of many 

 systems and much difference of opinion. There is now, however, a considerable approach 

 towards unanimity on the main lines of such classification, though differences still remain 

 with regard to some of the details. For a long period the Papilionidae were placed at the 

 head of the sub-order, and in so far as size may be a consideration, they would certainly 

 merit that distinction. Bates, however, proposed a classification based on the structure of 

 the legs, and especially on that of the tarsi of the front pair, and his arrangement still forms 



