410 A. J. NICHOLSON 
draw sperms into the saucer-shaped cavity of the apparatus. 
Here the sperms would be directed by the radiating ridges to 
the micropyle, and would then pass down the funnel and 
between the stopper and the inner wall to the protoplasm of 
the egg. 
When an egg is freshly laid on water it is nearly white, 
but after a few hours it becomes grey, and by morning it is 
usually, if not always, quite black. The whole of this change 
of coloration is due to the inner wall, which is transparent 
when laid but later becomes opaque black. In several cases 
insects in captivity have laid their eggs on dry media instead of 
on water, and in none of these cases did the eggs become black : 
they merely turned dirty yellow. It would thus appear that 
water has something to do with the productionof the dark colora- 
tion, though how the water gets to the inner wall is not clear. 
Besides changing colour the inner wall changes in character 
after the deposition of the egg. Ifa freshly-laid egg is placed in 
strong acid or alkali rapid expansion of the inner wall takes 
place, and it is seen first to become rapidly wrinkled and finally 
to burst through the chorion with explosive force. 
An egg which has become black, treated in the same way does 
not appear to be acted upon. Also if a freshly-laid ege is 
crushed under a cover-slip the inner wall is seen to be gelatinous, 
and oil-like globules may be broken off if a little pressure is 
applied. If treated with osmie acid these globules become 
brown, so that there may be a chemical, as well as a physical, 
resemblance between the inner wall and oil. If an egg which 
has become black is crushed it is found that the inner wall is 
no longer gelatinous, but is hard and somewhat brittle as it 
cracks with pressure. 
The yolk-mass occupies the whole of the egg inside the inner 
wall. It consists of an alveolar protoplasmic mass in the 
vacuoles of which volk granules of two kinds are found (fig. 11). 
The more obvious form of yolk consists of comparatively 
large granules 0-003 mm. to 0-01 mm. in diameter, which are 
proteid in character, as the following reactions show. 
If treated with copper sulphate solution followed by excess of 
