J. W. Jenkinson 
151 
It may be pointed out that since the two ends of the First Furrow are indistin- 
guishable from one another the range of the vahie of the angle between it and 
either the Plane of Symmetry or the Sagittal Plane does not extend beyond 90° in 
either direction. In the case of the other two planes however the two ends are 
externally unlike, the first having the grey crescent, the second the dorsal lip of 
the blastopore at one end. It is consequently possible to distinguish between any 
angle and its supplement, and the range of values may be extended on each side to 
180°. This has been done in Tables II. — V. and the results are entered in brackets 
in the second column of standard deviations in Table VI. 
TABLE VI. 
0- 
P 
■ 
First Furrow 
and 
Sagittal Plane 
(t) 
Plane of 
Symmetry and 
Sagittal Plane 
(^) 
Plane of 
Symmetry and 
First Furrow 
(«) 
First Furrow 
and 
Sagittal Plane 
(Pap) 
Plane of 
Symmetry and 
Sagittal Plane 
(Pay) 
Plane of 
Symmetry and 
First Furrow 
{P,y) 
1. E 
ggs close. Axes 
horizontal 
38-42° ±-70 
31-86'+ -56 
(42-29° ±-79) 
41 -59° ± -84 
-201 + -028 
-263 ±-027 
•118 ± -029 
II. 
Eggs close. Axes 
vertical 
33 -44° ±-44 
30-17°+ -51 
(36 -84° ±-62) 
39-72° ±-61 
-352 ±-021 
-276 ±-022 
-023 ± -024 
III. 
Eggs spaced. 
Axes horizontal 
33 -49° ±-96 
27-53°+ -84 
(29-37° ±-89) 
36-60° ±1-11 
-292 ± -039 
-399 ± -036 
•075 ± -043 
IV. 
Eggs spaced. 
Axes vertical 
31-45°± -73 
26-80°+ -82 
(31 -50° ±-96) 
34-46° ±1-07 
-364 ± -033 
-451 ± -035 
-186 ±-043 
It will be clear from these tables that both " pressure " (as I will call it, though 
it is doubtful as we shall see, whether pressure is the real cause of the disturbance) 
and gravity affect the relations between the three planes, for in all three cases the 
standard deviation diminishes while the correlation coefficient increases when both 
factors are eliminated (IV.). 
Taken separately however the two agencies do not modify the values of the 
angles between First Furrow and Sagittal Plane, and between Plane of Symmetry 
and Sagittal Plane in the same way. Thus it will be seen that in the first case 
the standard deviation is slightly less, the correlation coefficient greater when 
gravity alone is removed (II.) than when the pressure only is omitted (III.), while 
the agreement between the Plane of Symmetry and the Sagittal Plane is closer 
under the influence of gravity alone than of pressure alone, whether this agreement 
be measured by the standard deviation or by the correlation coefficient. The 
value of the standard deviation progressively declines in the case of the Plane of 
Symmetry and the First Furrow ; the correlation coefficient is somewhat in- 
explicably large when both agencies are allowed to interfere (I.). If the values of 
standard deviation and correlation coefficient be considered for each of these angles 
