ON THE RELATION BETWEEN THE SYMMETRY OF THE 
EGG, THE SYMMETRY OF SEGMENTATION, AND THE 
SYMMETRY OF THE EMBRYO IN THE FROG*. 
SECOND COMMUNICATION. 
By J. W. JENKINSON, M.A., D.Sc, Lecturer in Comparative and Experimental 
Embryology in the University of Oxfbi'd. 
PART I. 
In a paper published in Volume v. of this Journal I gave an account of the 
relation between three meridional planes in the egg and embryo of the common 
frog, namely, the Plane of Symmetry of the unsegmented egg (as determined by the 
position of the grey crescent which appears after fertilization), the Plane of the 
First Furrow of segmentation, and the Sagittal Plane of the embryo. 
The examination of the angles between these planes in a fairly large number of 
cases showed (1) that there was a fair tendency for the Sagittal Plane to coincide 
with the First Furrow since angles of small value considerably preponderated over 
those of large, but at the same time very little correlation between the two ; 
(2) that there was a greater tendency for the Sagittal Plane to coincide with the 
Plane of Symmetry, and some correlation between the two, the value of the 
standard deviation from the mean (approximately 0°) being less, that of the corre- 
lation coefficient greater than in the former case ; (3) that the First Furrow tended 
to lie either in or at right angles to the Plane of Symmetry, and that there was 
little correlation between the two. 
* I should like to take this opportunity of expressing the great obligations I am under to Professor 
Pearson for the trouble he has taken iu suggesting methods of dealing with the data. I have also to 
thank Mr Schuster for correcting some of the arithmetic. I may say, perhaps, that the delay in 
publication is due to the fact, first, that the experiments have extended over three years, and secondly, 
that the working out of the results — especially those of Part II.— has involved a good deal of labour. 
In cutting the necessary sections I had assistance, thanks to a grant of money from the British 
Association. 
