,«,,. RECENT OBSERVATIONS UPON MIMICRY. 15 



which would probably be inclined, in the absence of their favourite 

 insects, to drop the prejudices which they are supposed to entertain 

 against brightly coloured moths. 



The mimicry shown by the Sesiidae (Clearwings) and by Leptalis 

 and some other genera of the Pieridae is less striking, inasmuch as all 

 the members of the family or genus, as the case may be, have moved 

 in the same direction. The very fact of the absence of scales from the 

 wings of the Sesiidae constitutes in itself a considerable step in the 

 direction of resemblance to a bee or fly. It can hardly be assumed 

 that each species of Sesia independently copied some Dipteron or 

 Hymenopteron, first of all losing its scales and then becoming 

 modified in colour and size, habits, lS:c. The development of this 

 family of moths shows that the scales are partially formed during the 

 pupal stage, but that they are arrested before they reach their full 

 size, and then disappear. The study of the development of animals 

 always shows, with more or less clearness, an epitome of the history 

 of the race. Every animal, as it has been put, " is compelled to 

 climb up its own genealogical tree." Thus these moths are evidently 

 derived from scaled moths. A tendency to lose the scales characterises 

 other families of Lepidoptera besides these Sesiidae ; and it is at least 

 a reasonable supposition that this tendency may have been accentuated 

 by the need for protection. 



The principal difficulty in taking this view is the singular unani- 

 mity which the very numerous species of this group have shown in 

 their choice of a disguise. As these insects are found in most parts of 

 the world, and have, therefore, to cope with all kinds of hindrances to 

 their prosperity, it might have been thought that they would display 

 a corresponding variety in the methods by which these disadvantages 

 are overcome. One is tempted, therefore, to believe that this family 

 of moths were moulded into their present form by causes of which we 

 know nothing, and that to the very considerable initial likeness to 

 the Hymenoptera generally, such special resemblances as they show 

 to particular bees and wasps, were added later through the action of 

 Natural Selection. 



Much more striking as evidence of the truth of Mr. Bates' 

 theory are such cases as Basilavchia hipparckus. This genus of but- 

 terflies, with the exception of the species mentioned, are dark 

 coloured with blue spots round the margins of the wings ; B. hip- 

 parcJius is tawny-brown and black, closely simulating in tints and 

 plan of colouration the Danaid Anosia plexippiis. If this Danaid is 

 really avoided by birds, we can understand why the Basihurhia has, 

 so to speak, diverged from the road it ought to have followed, and 

 imitated the Anosia. On the theory of mimicry, we interpret this 

 divergence as due to Natural Selection gradually acting on a small 

 initial difference ; and if an insect is found whose colouration is 

 strikingly unhke that of its immediate allies, it is apt to be assumed that 

 another insect will be found which it imitates. But this assumption 



