32 CARL GOTTFRIED HARTMAN 



be noted from a study of wax models of such eggs. In models 

 of eggs from the 6- to the 16-celled stages the blastomeres are 

 grouped into pairs of common origin. Thus a 6-celled egg has 

 two large cells and two pairs of small cells, that is, 2 + (2 x 2) 

 = 6. Likewise, a 10-celled egg has six large and four small 

 cells, or 6 + (2 X 2) = 10. If lines be drawn connecting the 

 centers of the cells of each pair, scarcely any two lines are 

 parallel (text fig. 3). 



One need not rely upon wax models, however, to note that the 

 cleavage planes are no longer parallel. Several eggs were fixed 

 at the time two or more of their blastomeres were in mitosis and 



A B 



Fig. 3 Sketches of wax models during fourth cleavage. .4, 10-celled egg No. 

 85 (18) a; cells 1 and 6 and 3 and 4 are pairs of cells of common origin; cells 9 and 

 10 are in mitosis. B, 12-celled egg No. 85 (18) b; the four pairs of smaller 

 daughter Cells are easily recognized in the figure; cells 5 and 6 are in mitosis 

 (fig. 21) (X 330). 



from the direction of the spindles the angle of the cleavage planes 

 may be determined. This is strikingly true of three eggs con- 

 taining 8, 10 and 12 cells respectively (text figs. 2 B, and 3 A 

 and B). In the 8-celled egg (text fig. 2 B) two cells are in the 

 telophase stage of division, the nuclei of the daughter cells under- 

 going reconstruction; five cells are in metaphase or beginning 

 anaphase with the chromosome-loops clearly seen at or near 

 the equator of the cells; one cell is in the resting condition. 

 The directions of the spindles obey no apparent rule except 

 that these are tangential to the surface of the egg, as the mitotic 

 figures show. 



