J. W. Jenkinson 
In Table XVII. the values of the standard deviations, as calculated by my 
method, are given. It appears that the relation between First Furrow and Sagittal 
Plane and between First Furrow and Plane of Symmetry is closer when the eggs 
TABLE XVII. 
Values of <t 
First Furrow 
and 
Sagittal Plane (7) 
Plane of Sym- 
metry and 
Sagittal Plane 
Plane of Sym- 
metry and 
First Furrow (a) 
A. In light throughout 
Bn. In darkness till segmentation 
B /3. In darkness till dorsal lip 
38-55° ±1-39° 
32-.30°±-88° 
32 -92° ±-89° 
30-24° + 1-0.5° 
(38- 77° ±1-3.5°) 
30-99°+ -81° 
(41 -55° ±1-09°) 
.32-88°+ -88° 
(.38-83° ±1-03°) 
.39-45° ±1 -.36° 
35-63°± -96° 
37 -65° ±1-01° 
are kept in darkness (B) than when they are exposed to light throughout (A). 
There is practically no difference, as estimated by this method, in either of the.se 
relations between the eggs exposed to light after segmentation has begun (B a) 
and those kept in darkness till the end (B ^). 
The action of light on the other hand appears to improve the relation between 
the Plane of Symmetry and the Sagittal Plane when the range is limited to 90° 
on each side*. 
If, however, the range be extended to 180° on each side (the figures in 
brackets) then the tendency of the Sagittal Plane to lie in the Plane of Symmetry 
appears to be greater when the eggs are kept permanently in the light (A) or in 
the darkness (B y8) than when the Symmetry Plane is developed in the darkness 
but the Sagittal Plane under the influence of light (B a). 
It will be noticed that the value of a is in each ca.se smaller for (3 than for 7 
and for 7 than for a in conformity with previous results (Tables I. and VI. IV.). 
The absolute values are however larger. This must be due to some peculiarity 
of the eggs, or of the breeding season. 
In Table XVIII. are shown the correlation coefficients (Pearson's method). 
The correlation between First Furrow and Sagittal Plane (/3„^), and that between 
First Furrow and Symmetry Plane (p^y) are both improved when the eggs are 
kept in darkness, at least in the positive series. The correlation between Plane 
of Symmetry and Sagittal Plane {pay) hardly alters, but appears to be slightly 
less when the eggs are kept in the light throughout (A). 
The correlations between the Plane of Symmetry and Sagittal Plane are again, 
always higher than those between First Furrow and Sagittal Plane. 
• This is due to the fact that while the grey crescent turns away from the light, the dorsal lip turns 
towards it, but that this difference of 180-' is ignored when the range is limited to 90°. 
