28 IXTRODLX'TIOX. 



Colour and Pattern. 



Few, if any, groups of beetles offer richer materials for a study 

 of the problems of colour and pattern than the Cetoniinm. 

 Black or dull-coloured species are exceptional and found only in 

 the Ckemasxociulixi and a few genera peculiar in their very 

 retiring or jiocturnal habits. Some, however, are of a highly 

 polished and lustrous black, relieved with patches of bright orange, 

 red or green, as in the genus Diceros, a sharp contrast which must 

 make them very conspicuous in almost any environment. In the 

 highly characteristic Indian group of the Heteeokeiiinides vivid 

 greens predominate and the surface is always very shining, 

 frequently glassy. This colouring is very variable, and different 

 individuals of a species may be grass green, olive green, indigo, 

 purple, blue, black, fiery red, or golden green. Such shades may 

 always be regarded as interchangeable and of no significance for the 

 purpose of classification. All the species, however, are not equally 

 variable, for while some shade of green is nearly always the normal 

 one, in some species other colours are almost ot equal frequency, as 

 for instance in Tortjnorrhina dlstincta and Httcrorrhiaa nigritarsis^ 

 and in others they are of rare occurrence, as in Heterorrhina 

 punctatissima and most species of Triffonophorus. Defect of pig- 

 ment in all these green species seems to result in the production 

 of fiery reds, and it is probable that the red condition is passed 

 through in the process of attaining the full colouring of maturity. 

 Experiment shows that it is produced in dead specimens by the 

 chemical decomposition which takes place in the green pigment 

 upon prolonged exposure to sunlight. 



In the Heteeokrhinides colour patterns do not occur, or only 

 in a few cases in tlie sha])e of large masses of yellow or black. In 

 the most typical Cetoxiix-E, represented by the genera Ceionia, 

 Protatia, C'J inter ia, etc., ])atterus are the rule and are due to a very 

 fine powdery substance genei-ally lying in and filling depressions 

 in the surface and therefore less easily worn off than is often the 

 case with similar powdery or scaly adornments. These decorations 

 are always white or some shade of yellow, occasionally approaching 

 red, and can almost always be traced to a primitive arrangement 

 of spots which recurs over and over again throughout the group. 

 The primary spots are a ])air placed transversely behind the 

 middle of the pronotum and four behind the middle of the elytra 

 in a transverse, but not a straight line. Secondary, and generally 

 smaller, spots constantly found are a pair before the middle of the 

 pronotum, a pair at the hind margin of each elytron, two or three 

 at the outer margin, and one or more near the scutellum on each 

 side. The spots have a marked tendency to lengthen and coalesce, 

 those of the thorax longitudinally and those of the elytra trans- 

 versely, forming irregular bands, of which one crossing the elytra 

 beyond the middle is always a prominent feature. The further 

 development of the bands produces a complex irregular network, 

 and finally, as in Protatia fusca, a fine cobweb of interlacing pale 



