2O4 THE EVOLUTION OF MAN. 



northern tropical line. The spherical egg now consists of 

 8 cells, 4 smaller, upper, or northern, and 4 larger, lower, 

 or southern. A meridian-furrow, starting from the northern 

 pole, now appears in each of the first four cells, each of 

 which falls into two similar halves, so that 8 upper cells 

 lie on 4 lower cells (Fig. 31, N). It is only later that the 

 four new meridian cells place themselves slowly on the 

 lower cells, so that the number mounts from 12 to 16 (F). 

 Parallel to the first, horizontal ring-furrow, a new ring- 

 furrow now appears, nearer the northern pole ; this, there- 

 fore, we may compare to the arctic circle. The result of 

 this is that we find 24 cleavage-cells : 16 upper, smaller 

 and darker, and 8 lower, larger and brighter (G). The 

 latter, however, soon separate into 16, for a third parallel 

 circle appears in the southern hemisphere ; there are, there- 

 fore, 32 cells in all (Fig. 31, H). Eight new meridian- 

 furrows now arise at the northern pole, and, first cutting 

 the upper, darker, cellular circle, afterwards intersect the 

 lower, southern circle, and finally reach the southern 

 pole. We thus find stages in which there are successively 

 40, 48, 56, and finally, 64 cells (/, K). The inequality 

 between the two hemispheres constantly becomes greater. 

 While the inert southern hemisphere, for a long time, does 

 not add to its 32 cells, the vigorous northern half of the 

 globe furrows itself twice successively, and thus parts into 

 64, and then into 128 cells (Fig. 31, L, M). In the stage 

 in which we now see the egg, there are, therefore, 128 

 .small cells on the surface of the upper, darker half of the 

 egg-sphere, and only 32 cells in the lower, brighter half: 

 160 cleavage-cells in all. The inequality between the two 

 .hemispheres increases yet further ; and while the northern 



