240 RECORD OF CURRENT RESEARCHES RELATING TO 



set of variously shaped organs, including a short tube, are the natural 

 consequences of the modes of life in the two groujis respectively. 

 The bees, and more markedly their ancestors, the fossorial wasps, 

 having to conduct digging and scooping opei'ations in the preparation 

 of their nests and the care of their young, only devote a small portion 

 of their time to the use of their essentially sucking organs ; hence 

 these are less and more slowly developed than in the butterflies, 

 whose existence is entirely occupied by the functions of reproduction 

 and feeding. In the one case the insect's energy is spread over 

 the various organs, in the other it is mainly concentrated upon one, 

 so that evolution has had free scope to work out the development of 

 the very specialized organ of the butterfly. 



While, however, it is easy to trace out the diflferent stages by which 

 the bee's mouth-apparatus has been attained, owing to their embodi- 

 ment in still living types, there remains a wide gap between the butterfly 

 and its ancestors the Phryganidse. This may be explained by the com- 

 paratively short period which may be supposed to have been occupied 

 by the evolution of the butterfly's proboscis, of which a hint seems to 

 be supplied by the development, in a genus (Nemognatha) of the 

 essentially gnawing group Coleoptera, of a trunk, similar both in 

 structure and mode of use to that of Lepidoptera. This fact was 

 noticed by Dr. Fritz Miiller in Brazil, in the case of a dark, glistening 

 blue species of that genus. The European species, N. chrysomelina, 

 has the maxillae considerably prolonged, but of the normal Coleopteran 

 structure, while in the other case they are distinguished from the 

 component halves of the Lepidopteran trunk only by their inability 

 to be coiled up. Thus within the limits of a single genus the transi- 

 tion is made from a biting to a sucking mouth ; a transition which, 

 to fill up the gap between the Phryganidse and butterflies, we have 

 had to assume to have been made by the ancestors of the latter group 

 of insects. 



Sexual Colours of certain Butterflies.* — Mr. Charles Darwin 

 points out that the males of several butterflies display beautiful 

 colours on their wings when viewed in front, in which position the 

 male would be seen by the female when approaching her. In Diadema 

 boUna the two sexes differ widely in colour. The wings of the male, 

 viewed from behind, are black with six marks of pure white ; but 

 when viewed in front the white marks are surrounded by a halo of 

 beautiful blue. The males of another genus, Apatura, exhibit most 

 magnificent green and blue tints only when viewed in front, and also 

 in several species of Ornithoptera the hind wings of the males are of 

 of a fine golden yellow when so seen only. Butterflies when at rest 

 close their wings, and their lower surfaces, which are often obscurely 

 tinted, can then alone be seen ; and this, it is generally admitted, 

 serves as a protection. But the males when courting the females 

 alternately depress and raise their wings, thus displaying the bril- 

 liantly coloured upper surface ; and it seems the natural inference 

 that they act in this manner in order to charm or excite the females, 



* ' Nature,' xxi. (1880) p. 237. 



