Spots and Stripes. 43 



eupheno it has dammed the colour up and ponded it between bar and 

 tip. An exactly intermediate case between these two species is seen 

 in A. eaphemoides, Fig. 10, Plate IV., in which the spot is elongated, 

 and dribbles off into an irregular band, into which the orange has 

 trickled, as water trickles through imperfect fascines. This series of 

 illustrations might be repeated in almost any group of butterflies, 

 but sufficient has been said to show how spots can spread into patches, 

 either by the spreading of one or by the coalescence of several. 



We will now take an illustration of the formation of stripes or 

 bars from spots, and in doing so must call attention to the rarity of 

 true stripes in butterflies. By a true stripe I mean one that has even 

 edges, that is, whose sides are uninfluenced by structure. In all our 

 British species such as P. machaon, M. artemis, M. athalia, V. atalanta, 

 L. sibilla, A. iris, and some of the Browns, Frittilaries and Hair- 

 streaks, which can alone be said to be striped, the bands are clearly 

 nothing more than spots which have spread up to the costae, and 

 still retain traces of their origin either in the different hue of the 

 costae which intersect them, or in curved edges corresponding with 

 the interspaces of the costae. This in itself is sufficient to indicate 

 their origin. But in many foreign species true bands are found, though 

 they are by no means common. Illustrations are given in Plate IV., 

 of two Swallow-tails, Papilio machaon, Fig. 11, and P. podalirius 

 Fig 12, in which the development of a stripe can readily be seen. 



In machaon the dark band inside the marginal semi-lunar spots of 

 the fore-wings retain traces of their spot-origin in the speckled 

 character of the costal interspaces, and in the curved outlines of 

 those parts. In podalirius the semi-lunar spots have coalesced into a 

 stripe, only showing its spot-origin in the black markings of the 

 intersecting costae; and the black band has become a true stripe, 

 with plain edges, Had only such forms as this been preserved, the 

 origin of the spots would have been lost to view. 



It may, however, be said, though I think not with justice, that 

 we ought not to take two species, however closely allied, to illustrate 

 such a point. But very good examples can be found in the same 

 species, A common German butterfly, Araschnia Levana, has two 

 distinct varieties, Levana being the winter, and prorsa the summer 

 form ; and between these an intermediate form, porima, can be bred 

 from the summer form by keeping the pupae cold. Dr. Weismann, 

 who has largely experimented on this insect, has given accurate 

 illustrations of the varieties. Plate V. is taken from specimens 



H 



