150 Symmetry of Egg and Symmetry of Embryo in the Frog 
to and fro, however carefully, some slight shifting might occur. I measured 
the first furrow in a set of eggs, then violently shook the slide and jogged it on the 
table, and then measured again. The difference in many cases, nearly half, was 
less tlian 3° and in no case very great*; and the eggs of course were never 
ordinarily subjected to such violent treatment. The eggs were always taken 
straight from the uterus, placed in rows on the slide, moistened with water, 
artificially fertilized, and allowed to remain in water until the jelly had become 
well swollen. They were then removed from the water and kept in a damp 
chamber till required. 
The following are the results of the measurements. 
The angle between the first furrow and the sagittal plane was determined 
in 889 cases, and in 397 of these the position of the plane of symmetry was also 
observed. In 14 other cases the angle between the plane of symmetry and 
the first furrow was found, in 112 other cases that between the plane of 
symmetry and the sagittal plane. There are thus 509 observations of the angle 
between the plane of symmetry and the sagittal plane, 411 observations of that 
between the plane of symmetry and the first furrow. 
I. First Furrow and Sagittal Plane. 
Table I. gives the frequencies for groups of 10°. 
TABLE I. 
First Furrow and Sagittal Plane. 
Groups of 10°. 
Class 
Frequency 
Class 
Frequency 
- 90—81 
27 
+ 0—10 
111 
80—71 
26 
11—20 
86 
70—61 
24 
21—30 
84 
60—51 
32 
31—40 
43 
50—41 
30 
41—50 
45 
40—31 
42 
51—60 
34 
30—21 
53 
61—70 
31 
20—11 
69 
71—80 
29 
10-0 
104 
81—90 
19 
889 
M= 2-12° ±-914 
o- =40-39° ±-646. 
* The actual frequencies of these differences were : 
Angle: 0° 1° 2° 3° 4° 5° 6° 7° 8° 9° 10° 11° 12°... 18° 
Frequency: 6 10 85952114 1 1 2... 1 
