170 Symmetrij of Egg mid Symmetry of Embryo in the Frog 
is not complete. As far as we have seen at present the correlation is great 
when gravity alone acts upon the eggs, and impresses upon them a symmetry 
which affects the position of the grey-crescent, and then that of the Sagittal Plane. 
We also know that the effect of light upon the Sagittal Plane (the dorsal lip) is 
not the same as its effect upon the grey-crescent, and that when the eggs are 
grown in darkness the agreement between the positions occupied by these planes 
in the egg is considerable (Figs. 2 and 3, I B, Tables XV. and XVI. I B). 
Now it is of great interest to observe, that in these circumstances, the standard 
deviation of the angle between Plane of Symmetry and Sagittal Plane is low, 
namely, 17*64° + 1'38 (Table XXIV.). If we except the solitary instance of an angle 
of 177" (which I feel sure is a mistake) there is no value greater than 60°, and only 
one greater than 45°. Of the 114 eggs in this series the position of the First 
Furrow was known, unfortunately, in only 37, but I have employed these in 
TABLE XXIV. 
Eggs Close. Axes Horizontal. Darkness. Plane of Symmetry and Sagittal Plane. 
Negative 
Positive 
90—75 
o 
1 
o 
so 
1 
80—15 
15-0 
7 
o 
1 
1 
■o 
1 
1 
Total 
6 
11 
.37 + 1* 
38 
12 
8 
1 
114 
* +177° M = l-32°±l-95 cr = 1704° ±1-38. 
making the correlation table (Table XXV.). The value of the coefficient is fairly 
high p = -642 + -040, and would have been higher still ('736 + -029) had I not 
halved the frequency of the one instance in which the angle between First Furrow 
and Sagittal Plane was exactly 90", though owing to the general trend of the 
correlation table it was perhaps hardly necessary to do this. Be that as it may, 
the correlation between Plane of Symmetry and Sagittal Plane is certainly greatest 
when gravity is allowed to act upon the eggs, but when light is eliminated. Under 
the same circumstances, the standard deviations (as calculated for this very small 
number) of the angles between First Furrow and Plane of Symmetry, and First 
Furrow and Sagittal Plane remain unaltered, or rather are slightly increased in 
comparison with the whole series (Table VI. I.). 
Yet it may still be questioned whether, even so, the First Furrow does not 
exercise some independent influence upon the Embryonic Symmetry, and slight 
though this influence may be, it must, I think, be allowed for, at least as a 
possibility. 
For even under these most favourable conditions, the correlation of egg-sym- 
metry with embryonic-symmetry is not as great as might be desired. On the 
