202 COLOUR IN NATURE chap. 



and conspicuous wings, and small or concealed 

 abdomen, the colour-markings occur on the wings or 

 wing-covers, and have thus no relation to segmenta- 

 tion. In this case the coloured structures are lateral 

 organs and not parts arranged in linear series, but 

 they conform again to the rule that organs occupying 

 similar positions display similar coloration ; the two 

 fore-wings display similar colours, and the hind agree 

 with one another and may agree with the fore-wings. 

 On these points there are some interesting observa- 

 tions by Mr. Scudder, whose statements have been 

 confirmed and amplified by Mr. A. G. Mayer. In 

 discussing the butterflies of North America, Scudder 

 showed that the number of instances in which similar 

 markings appear in the same areas in the two pairs 

 of wings is too large to be due merely to coincidences. 

 The process is most readily traced in the case of 

 ocelli, which usually tend to be similar in size and 

 position, and to be situated between the same 

 branches of homologous veins. In summing up his 

 own and Scudder's observations, Mayer (1897) lays 

 down the following statements with regard to colour- 

 patterns in butterflies : — 



1. "Any spot found upon the wings tends to be 

 bilaterally symmetrical both as regards form and 

 colour, the axis of symmetry being a line passing 

 through the centre of the interspace in which the spot 

 is found, and parallel to the direction of the longi- 

 tudinal nervures." 



2. "Spots tend to appear not in one interspace 

 only, but as a row occupying homologous places in 

 successive interspaces." 



It is thus seen that the wings and their homo- 



