AMEBOID MOVEMENT 69 



the amount of ectoplasm in the process of forming at any given 

 moment could be compared with a similar relation existing in 

 discoides, to see whether these respective ratios were propor- 

 tional to the speed of the moving surface films in the two amebas. 

 As it is, the irregularity of form of sphaeromicleosus makes such 

 computation subject to the possibility of considerable error. In 

 discoides however the problem is comparatively simple. I there- 

 fore did not go into this matter extensively, but merely worked 

 out the relations mentioned in one case, and I mention it here 

 to illustrate the method rather than to record the result, which 

 is not to be taken as very exact. 



Since the movement of the surface film is obviously a surface 

 phenomenon, only the surfaces of the amebas need to be taken 

 into account. In Figure 28 is illustrated a discoides of such a 

 shape as to allow a fairly accurate computation of its surface. 



Figure 28. A clavate Amoeba discoides, showing the amount of ecto- 

 plasm that is constantly being made at the anterior end. Length of the 

 ameba, 310 microns. 



Three outlines of the anterior end only are given ; the rear por- 

 tion of the ameba remained approximately the same size and 

 shape in the three outlines. The cross lines at the anterior end 

 divide the forming ectoplasm of the ameba from the formed. As 

 will be noticed the cross lines are drawn through the intersections 

 of two successive outlines. Computing the areas on both sides of 

 the cross lines for the two outlines and averaging them, there is 

 found a ratio of i to 10; one-eleventh of the total surface repre- 

 sents forming ectoplasm, and ten-elevenths formed ectoplasm. 

 (One-twenty-second of the total surface was deducted for surface 



