43 
which may he found in every egg by patient watching. It is. 
of very short duration, and the limiting membrane usually 
becomes smooth again in about fifteen seconds after the con- 
tractions commence. Before I discovered that similar waves 
run over the surface of the egg for a few seconds at the begin- 
ning of the active changes at later stages of segmentation, I 
naturally inferred that they were connected with the extru- 
sion of the polar globules. While it seems probable that they 
are in some way connected with this extrusion, their occurrence 
at later stages show T s that this is not their only significance. 
So far as I am aware, this is the first notice of their occur- 
rence. 
Soon after the waves commence, an area, which is a little 
less granular than the mass of the egg, becomes visible at the 
formative pole, and from this the first polar globule soon 
begins to protrude, pushing out the external egg-membrane. 
Figure 3 is the same egg two minutes later, and Figure 4 is 
the same after another interval of two minutes. The oval 
outline is now gradually changing to a pear- shape, the stalk 
of the pear occupying the nutritive pole, and the polar 
globule projecting from the middle of the broad end of' 
the pear at the formative pole. During these stages the 
granular matter of the yolk may be seen to flow in a steady,, 
slow current, around the periphery of the egg, but, as far as I 
could observe, the current has no definite starting-point or 
terminus. At these stages there are no waves on the surface, 
and the membrane is smooth. It is interesting to observe 
that while these changes are taking place the nutritive end of' 
the egg grows a little more transparent than the formative 
end, a reversal of what occurs in almost all other eggs which 
pass through unequal or irregular segmentation, although 
Loven has described the same phenomenon in Crenella. In 
a short time three planes of cleavage run in towards the centre 
of the egg from three equidistant points on the periphery, as 
shown in Figure 5, which is two minutes later than Figure 
4, although the changes usually take place much more rapidly. 
One of these planes is at the point occupied by the polar 
globule, and the others about midway between it and the 
