the assumption, that unicolourism (self colour) is a Secondary feature, 
originating from the effacing of a pattern of spots. Of the way in 
which this is effected Platensina ampla gives us a good idea. 
As remarked abovt, pk Meijer calls the shade of the abnormal spots 
light brown, when seen in a certain direction, but he leaves un- 
determined, what direction this is. Now [ found, that the colour is 
very different according to its being observed in reflected or trans- 
mitted light. Seen in the latter, the spots are actually brown, but 
with the first mentioned illumination they are light blue with a 
hazy lustre. Besides this there is a difference, if the transmitted 
light is made to pass straight at full strength, or obliquely and in 
moderate quantity. Only in the latter case the spots stand out clearly 
against, their dark surroundings, showing a light-brown shade, and 
are clearly seen to transmit more light than the rest of the wing- 
surface. In strong and directly transmitted light on the contrary 
they hardly contrast with the surrounding dark wing-membrane, 
and can only be distinguished from it by a somewhat lighter ring 
round a darker core. By means of all three methods of observation, 
however, we may establish the hairs in the area of the blue spots 
to be colourless, just as above the hyaline spots. | 
L therefore agree with pr Meijers, that the absence of colouring 
matter in the hairs within the precincts of the dead spots, contributes 
to their lighter shade, and that this shade furthermore proceeds 
from a scantier quantity of brown pigment in the wing-membrane. 
Sull I wish to make a distinction between these two causes in so 
far that I ascribe the whitish-blue lustre of the spots more especially 
to the first, their hazel-brown shade in weak and obliquely trans- 
mitted light on the contrary to the second. 
The occurrence of these dead spots therefore provides us with 
anew argument for asserting that in the order of Diptera the 
different colour-patterns stand in genetical interrelation, and for 
opposing DE Mmurrr'’s inference, that they are absolutely independent 
of each other. 
On p. 70 (at the bottom) pr Meijer again mentions a case of 
two different kinds of spots in a Trypetine fly, viz.: “Tüpfelflecke” 
in the dark transverse bars, which in several species (especially those 
related to the genus Tephritis) should be distinguished by shade as 
well as by localisation from the common hyaline spots situated 
between these bars, which are considered by pr Mriuere as remnants 
of the original unbroken hyaline wing-surface. 
The author does not mention the species he means, so that I 
cannot tell precisely which cases he has in view. But if, as I presume, 
74 
Proceedings Royal Acad. Amsterdam. Vol. XIX 
