308 



THE FORMS OF TISSUES 



[CH. 



centres from the points of intersection of the circular arcs, will 

 always enclose an angle of 60°. Again (Fig. 115), if we make the 

 angle c"uf equal to 60°, and produce uf to meet cc" in /,/ will be 

 the centre of the circular arc which constitutes the partition Ou ; 

 and further, the three points/,^, h, successively determined in this 



I 



Fig. 115. 



manner, will lie on one and the same straight line. In the case 

 of coequal bubbles or cells (as in Fig. 114, B), it is obvious that 

 the lines joining their centres form an equilateral triangle; and 

 consequently, that the centre of each circle (or sphere) lies on the 

 circumference of the other two ; it is also obvious that uf is now 



