role of dorsal appendages

[Graham Thomas]

Dear Fly People,

        I am curious about the function of the dorsal appendages on the
chorion of Drosophila eggs. I have always been told that they are/might be
'for respiration' but the knowledge always seems anecdotal and never first
hand knowledge. What is actually known about the role of these structures?

        This is not really my area of specific interest, but I am motivated
to ask after leaving a grape plate in the fridge over the weekend and
noticing that the flattened area at the end of the appendages seems to be a
very efficient condensation nucleus for water vapour. The plates were moved
from 25C to 4C with a petri dish lid in place; conditions that presumably
favour condensation of moisture evaporating from the dish. (We are all
familiar with the 'misting' of a petri dish lid when put a 4C). However,
most of the eggs nucleated (and held) a neat drop of water at the end of
both dorsal appendages. Is water condensation a known/speculated function
for these objects?

        Just curious.

        Graham Thomas


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     Graham Thomas,
     Departments of Biology and Biochemisty/Molecular Biology,
     The Pennsylvania State University,
     208 Mueller Laboratory,
     University Park, PA, 16802

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