II. I 



CELL-DIVISION 



49 



In the other types radial and bilateral the principle of least 

 surfaces is obviously disobeyed, for here four or more surfaces 

 meet in one line and at angles other than 120. 



Roux (1897) has, however, shown that if a certain condition 

 be imposed on the system of lamellae, figures may be produced 

 which very closely resemble the patterns presented by radially 

 and bilaterally segmenting ova. This indispensable condition 

 is that the system shall be surrounded by a rigid boundary, as 

 the eggs themselves are by a membrane. Roux ; s system was 

 made by dividing into two, four, and eight a drop of paraffin oil 

 suspended in a closely fitting cylindrical vessel between alcohol 

 and water. To this medium was added calcium acetate to prevent 

 the drops reuniting. The drop was divided with a glass rod. 



FIG. 26. Koux's oil-drops. A and B, the drop divided equally ; C and 

 D, unequally. Each of the two equal drops divided equally in E, 

 unequally in F. (From Korschelt and Heider, after Roux.) 



When the two drops formed by the first division were equal 

 the surface of contact was flat, when unequal convex towards 

 the larger one, in accordance with the rule (Fig. 26 A-D). 



When the second was also equal, four drops were formed with 

 four surfaces of contact meeting in one line, or enclosing between 

 them a small 'segmentation' cavity. If the division of the 

 two equal drops was unequal, and the smaller cells adjacent, they 

 pushed into the larger ones ; the result, in fact, was the same 



