378 



THE FOEMS OF TISSUES 



[CH. 



set forth a few aggregates of eight cells, mostly from drawings of 

 segmenting eggs. In some cases they shew clearly the manner 

 in which the cells meet one another, always at angles of 120°, 



Fig. 165. (a) Part of segmenting egg of Cephalopod (after Watase); 

 (6) probable actual arrangement. 



Fig. 166. (a) Egg of Echinus; (b) do. of Nereis, under pressure. (After 

 Driesch). 



Fig. 167. (a) Egg of frog, under pressure (after Roux); (6) probable 

 actual arrangement. 



and always with the help of five intermediate boundary walls 

 within the eight-cell«d system; in other cases I have added a 

 slightly altered drawing, so as to shew, with as little change as 



