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1240 THE I5UTTERFLIES OF XEAV ENGLAND. 



owes a part of its \iiricty and enlivenment to excliange of some of these 

 tubercles for bright colored spots ; these break up the transverse black 

 stripes in a variable degree, and the stripes themselves appear to be but 

 little more than retention of parts of the original color (fixed at the particu- 

 lar spot they occupy by the central position of the black tubercles) when the 

 gi'ccn livery of adult life is assumed. For it seems to be a green rescm- 

 l)ling the green of the leaves upon whicli the caterpillar lives, that is the 

 ultimate aim of most Papilionid coloration. In caterpillars of their size 

 other colors would be too conspicuous for their advantage and variation in 

 this direction would be natui'al. Moreover, it is the color reached or partly 

 reached, in several different ways, as the development of the other types 

 show ; thus in the other striped caterpillar, Iphiclides, the stripes grow obso- 

 lescent toward maturity and leave the caterpillar more completely green. 



We may tlien trace several lines, to a certain extent parallel, along 

 which the modification of the caterpillars of Papilioninae has developed, pai- 

 allcl at least in that the loss of the juvenile bristles has been unlvei'sal but 

 at different stages ; also that the loss of the juvenile tubercles has been uni- 

 versal though not always complete, their loss being generally made good 

 bylenticles and these by spots ; and sometimes, by acceleration, a phyletic 

 stage is set further and further Inick and finally, perhaps, crowded out. 



One of these lines, very distinct from the others, is found in Laertias, 

 which has developed to so high a degree that its juvenile bristles, them- 

 selves excej)tionally simple, are completely lost with the earliest stage; so, 

 too, most of the tubercles ; but here a very curious change occurs : those 

 which are lost are replaced in new positions by others entirely different, 

 which take on a more elongated form and become more properly fleshy fila- 

 ments ; while those which remain assume also the new development. The dark 

 and almost uniform color of the lar^■a throughout life is to be explained prob- 

 ably by acceleration ; it is the mature color thrust back into the juvenile stage, 

 to the obliteration of any trace of the saddle which once may have prevailed 

 there ; and is in keeping with the present almost complete assumption of 

 the mature characters at the second larval stage. In support of this posi- 

 tion I would point out that traces of the saddle still exist in the mature 

 forms of other filamentous caterpillars of Papilioninae allied to Laertias, — 

 Ornithoptera, Menelaides, etc., indicating a still larger development of the 

 same in the earlier stages of the types with which, unfortiniately, we are 

 not yet acquainted. In Laertias, then, the saddle has been crowded back 

 out of existence. 



Another line of nearly as high development we find in Iphiclides, where 

 the extraordinary bristles and tubercles are lost with the very first stage 

 and maturitj' marks the second. Here again no saddle appears, the only 

 trace of it left being in the slight deepening of the color in the new-born 

 caterpillar near the extremities of the body ; here I conceive that the phy- 



