196 Symmetry of Egg and Symmetry of Embryo in the Frog 
Under the contrary conditions the value of the coefficient is /) = '479 ±*070 
(Table XLIV. a) which rises to -725 + "064, and -880 f '040, as first those instances 
are excluded in which the path turns away from the Furrow (Table XLIV. h) and 
then those also in which the path is parallel to the Furrow or in it (Table XLIV. c). 
It may be noted that, when the eggs are close and their axes horizontal, there 
is still no correlation even under what appear to be the most favourable circum- 
stances (Table XLIIL h). 
I am well aware of the doubtful value of a correlation determined on so very 
few examples, but, if the results can be accepted, it is evident that when the path 
makes a wide angle with the Furrow, the deviation of the grey crescent from the 
Furrow is large too. 
More direct evidence can, however, also be brought forward in support of this 
conclusion, for from the known values of the angle between Sperm-path and First 
Furrow, and First Furrow and Plane of Symmetry, the values of the angles 
between Sperm-path and Plane of Symmetry may be obtained. The results are 
given in Table XLV. in which the standard deviations are shown (the difference 
between negative and positive angles being neglected). In the same table the 
values of a, calculated in the same way, for the angle between Sperm-path and 
First Furrow are given for comparison. 
It is evident at once that when all cases are considered the relation of Sperm- 
path to First Furrow is as close as its relation to Symmetry Plane, if not closer ; 
that when the Sperm-path is included in or parallel to the First Furrow its 
relation to the Symmetry Plane is as in all the cases taken together ; that when 
the path is turned away from the Furrow its relation to the Furrow is much closer 
than to the Plane of Symmetry, but that when it is turned towards the Furrow the 
reverse is the case. 
If, however, the numbers are considered to be so small that this result must be 
rejected, then it must be confessed that no internal factor has yet been discovered 
by which the direction occupied by the plane of the grey crescent is conditioned ; 
nor am I able to see by what known internal factor it could be conditioned since, 
as far as I am aware, every possible cause has been tried. Provisionally, therefore, 
we must regard the direction of the whole (" penetration ") Sperm-path as the cause 
which determines, in the absence of all outside interference, the Plane of Symmetry 
of the unsegmented egg, and so the median plane of the embryo. 
The foregoing investigations have established a very close relation between the 
point of entrance of the spermatozoon, or the path taken by the spermatozoon in 
the egg, and the position of the First Furrow of segmentation. The relation is 
closest when the influence of gravity is removed by placing the eggs upon the 
slides with their axes vertical and their white poles below, but it still exists in a 
degree which cannot be ignored when the axes are horizontal ; indeed, if it be 
measured by the correlation coefficient instead of by the standard deviation it is as 
