168 Symmetrij of Egg and Symmetry of Emhryo in the Frog 
standard deviation is the same in the two cases. This is the result already 
obtained (Table XIV. IV.). 
In the case of the Plane of Symmetry (Table XXII.) there are high frequencies 
about 0"" in both light (A) and darkness (B) and again about 180° in darkness. 
These high frequencies are probably due — at least I can think of no other explana- 
tion — to the manipulation. In placing the egg on the slide each one was taken up 
by its jelly in the forceps, being seized near the animal pole, placed first with its 
axis at right angles to the slide (i.e. in the direction 0° to 180") and then turned 
into position with the axis vertical and the white pole below. It appears that the 
structure of the egg is unavoidably affected by this treatment, and a slight bilateral 
symmetry conferred upon it which is not without influence on the position of the 
Symmetry Plane. Similar high frequencies have been noticed already (Table XV.) 
and will be found to recur in the position of the Sagittal Plane. Obviously they 
cannot be attributed to the action of the light. 
TABLE XXII. 
Plme of Symmetry. 
Angle 
A. Light, 
(from -90°) 
B. Darkness 
- ISO— 150 
10 
56 
150—120 
13 
23 
120—90 
14 
40 
90—60 
12 
55 
60—30 
30 
57 
30—0 
28 
103 
+ 0—30 
33 
101 
30-60 
18 
57 
60—90 
11 
49 
90—120 
17 
46 
120—150 
19 
56 
150—180 
18 
60 
Totals 
223 
703 
The influence of the light upon the position of the grey-crescent is indeed in 
this series very doubtful indeed. 
The evidence that the Sagittal Plane is affected by this agency is, however, 
better (Table XXIII.) for when the eggs were exposed to light from the beginning 
of the segmentati(m until the appearance of the blastopore (B a) there is a slight 
rise in frequency between — 60° and — 90°, a rise which does not occur when the 
eggs remain in darkness (B /3). This is in agreement with the result already 
arrived at (Table XVI.), that the dorsal lip tends to turn towards the light. 
The high frequencies about 0° must be referred, as already explained, to the 
manipidation of the eggs. 
