384 T. H. MORGAN AND Um6 TSUDA. 



tion of pigment as found in the eggs ofRana temporaria, but 

 the eccentricity in its distribution in respect to the axis of 

 cleavage was greater than in eggs of Rana temporaria. The 

 egg looked at from above (with one pole of the axis turned 

 directly upwards) showed on one side a distinct white crescent, 

 as seen in fig. i. 



The most interesting fact is that in the thirty-two-celled 

 stage a very decided irregularity of the segmentation spheres 

 of the upper portion of the egg is to be found. 



This is readily seen in the three figures of the same egg 

 drawn in figs, i — iii. The first of these (fig. i) shows the egg 

 from above; eight cells lie along a line (four on each side) that 

 corresponds presumably to the first cleavage plane. These upper 

 eight cells are all approximately the same in size in this egg. 

 The eight cells forming the zone around the egg below the 

 upper eight, and which are sister cells with the latter, show a 

 difference in size on opposite sides of the egg, as shown in 

 figs. II, III. The difference may be seen from above, but still 

 better by a study of the opposite (lateral) sides of the egg. 



The lighter side of the egg is shown in fig. iii, in which the 

 border line of black pigment extends only for a short distance 

 over the side of the egg. The dark side of the egg is drawn in 

 fig. II, and here the pigment extends much further into the 

 lower hemisphere. On the light side of the egg (fig. iii) the 

 cells of the second and third zones are smaller than the cor- 

 responding cells on the opposite side of the egg (fig. ii). Un- 

 fortunately the four-, eight-, and sixteen-celled stages of these 

 eggs were not preserved, so that I am unable to say how far 

 back this difference in the two sides may be present. 



This led to a re-exaraination of the eggs of R. temporaria. 

 Here I found that at the eight-celled stage in most eggs one 

 of the four upper cells is somewhat smaller than its upper 

 vis-a-vis. It was also found that this smaller cell is the cell 

 nearest to the highest point reached by the white crescent; 

 therefore it must have come from that cell (now) of the lower 

 pole that contains the least pigment. At the sixteen-celled 

 stage those cells on the side of the egg nearest the upper limit 



