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- 
