122 ON COLOUR 



(pi. D, 27), as are also nearly all those which have 

 red bands. With, the exception of the males of 

 three species of Halictus, and both sexes of three 

 or four species of Andrena, all the red-banded 

 forms belong to the genus Sphecodes (pi. B, 11), 

 which is a cuckoo genus. The red coloration 

 occurs chiefly on nearly naked surfaces ; this is 

 specially noticeable in those bees which have 

 two varieties, such as Andrena rosce, one dull 

 coloured and the other red-banded : in these cases 

 the dull form is hairy and the red nearly naked. 

 The greatest proportionate number of banded 

 species occurs amongst the fossors, and these are 

 seldom clothed with hairs to any extent. These 

 bands seem to me probably to depend a good 

 deal on retarded development. Dark and 

 hairy bands, both as a rule, follow the joints 

 of the segments, as stated above. I only 

 say as a rule, as there are many where 

 the banding does not follow this principle, 

 but in far the larger majority the bands, 

 whether of dark colour or hairs, are apical. As 

 the segments overlap at the joints it is evident 

 that their discs would tend to mature more 

 rapidly than the overlapping bases and apices, 



