BILATERALITY OF THE PIGEON's EGG 



303 



This constancy of the axis angles in the eggs of a given bird 

 gives further support to the thesis that has been maintained 

 throughout this paper, namely that this relation of axes is deter- 

 mined by factors which are themselves expressions of the bilateral 

 organization of the egg; that is to say, the organization expresses 

 itself in a most constant fashion in the eggs of a given bird. If 



125° 



Diagram IV Two curves illustrating the variability in the relation between 

 the embryonic and long axes in the pigeon egg. 'A ' was plotted from observations 

 on 299 eggs. They were grouped in 5 degree classes and the number of eggs in a 

 class is plotted on the ordinates, the angles on the abscissae. There are three 

 modes in the 'normal' curve (see text), at 50, 70 and 90 degrees. The broken line 

 at the right represents the angles of the eggs laid by two birds whose norm was 

 above 90 degrees. B (the heavy line) is a curve plotted in a similar way from obser- 

 vations on 59 eggs in stages previous to the third cleavage. The angle measured 

 was between the shorter axis of the blastodisc and the long axis of the ovum. The 

 similarity of the two curves is obvious. 



this be true, the nucleo-cytoplasmic relation (diagram II B) in 

 the younger oocytes of a given ovary should correspond to the 

 axis angles in the eggs laid by the same bird. The ovaries of 

 only two of the birds in which a norm had been established, were 

 studied; one was no. 2 mentioned above, the other a bird whose 



