88 



it. So too, are the two small ones originating from tlie 

 smaller cell of the stage shown in Fig 5. The notch 

 which is moving inwards to nip oif the small cell from 

 the large one moves so fast that I find the camera lucida 

 of use only so far as it enables me to get the dimensions. 

 In like manner the contour lines on the other side are 

 rapidly changing in the division of the smaller cell. 

 Then follows a condition of rest shown in 

 Fig. 7. The micromeres are now three in 

 number, themegamere is still much greater 

 in bulk than all three. The nuclei again 

 become defined. The egg is passing slowly 

 into the stage shown in Fig. 8. at the one 

 pole of which we still see the i:)olar cells 

 The three micromeres have 



Figure 7 

 persisting. 



subsided : become depressed and the whole |^ 



outline is more rounded, like that of the M 



)%* 

 nnseo;mented eoo-. The faint indication of M 



a segmentation cavity or space shown be- "^^ 

 tween the micromeres and megamere in 

 Fig. 7, has disappeared. The embryo is Figure 8. 

 quiescent and has reached the limit of perhaps its third 

 or fourth period of activity and rest. The succeeding 

 stage represented in Fig. 9 is Avhere the next 

 period of activity has reached its comple- 

 tion. The micromeres of Figs. 7 and 8 have 

 again divided and one or two micromeres 

 have been derived from the megamere ; in 

 this way a number of additional micromeres 

 Figure 9. has been the result. The micromeres are 

 now piled up at one side, or rather end, of the egg^ and 

 the polar cells still persist. The micromeres display a 

 certain symmetry of arrangement. It now becomes ap- 

 parent that the micromeres are to be the foundation of 

 the epiblast or skin layer of the embryo, while the mi- 

 cromere is to become the hypoblast or inner layer from 



