200 Symmetrjj of Egg and Symmetry of Embryo in the Frog 
On this view the acrosome and the middle piece are both hygroscopic particles, 
and it is interesting to remember that they are both of centrosomal origin, the 
one being derived from the centrosphere, the other from the centrosome of the 
spermatid. 
This hypothesis is, it seems to me, very much strengthened by the result of 
a simple experiment. By placing a hygroscopic particle — a small crystal of salt 
or sugar for example — in a drop of the yolk of a Hen's egg, an imitation Sperm- 
sphere may very easily be made. A clear area from which the yolk granules have 
been driven away appears round the particle, and as the latter begins to dissolve 
it soon comes to lie in a little pool or vacuole of its own solution. 
Should this interpretation of the processes observed in the egg during fertili- 
zation be correct, it would seem obvious to connect the immigration of the 
pigment with the streaming movements of watery substance so set up, the focus 
towards which the streams are directed being in that case the whole (" penetration ") 
C D 
Fig. 7. The formation of the grey crescent. 
In A and C it has not yet appeared. 
A, B, the egg seen from the side. C, D, from the vegetative pole (centre of the white area). 
Sperm-path — the entrance-funnel and Sperm-sphere. It is with this that the 
direction of the Symmetry Plane appears to be correlated when gravity is not 
permitted to exert its influence. When gravity does operate the correlation dis- 
appears, and intelligibly so. For the movements due to the sinking of the yolk, 
the rising of the cytoplasm and pigment which we have known to be produced 
ever since Born described them in tlie permanently inverted eggs of Pfliiger's 
experiment, will evidently alter the direction of the other movement directed 
