1146 
a dark or a light streak extends over the middle of several inter- 
nervural cells, with which in the first case the dark nervural spots, 
in the second the light ones may be connected. This distribution of 
the colour therefore brings about two different effects: when the 
median is dark the uncoloured areas present themselves as light 
Fig. 5. Sciomyza javana (de Meyere). 
Fig 6. Traginops orientalis. 
spots on a coloured background, when it is light the pigmented 
areas form dark spots on a light field. Yet both patterns are varieties 
of the same groundplan, as may be seen by comparison of different 
species belonging to the same genus; e.g. Tetanocera vittigera, 
showing dark spots on a clear wing-surface and T. umbrarum, with 
light spots on a dark ground. But the same conclusion can be drawn 
from the consideration of different areas of the same wing: one 
internervural cell containing a dark median bar with light spots 
at either side, a neighbouring one the opposite arrangement, or 
even the proximal half of one such cell differing in this respect 
from the distal one. 
Though number as well as size of the spots is found to be incon- 
stant, I am inclined to assume, that also in these respects a funda- 
