No. 3-] PODARKE OBSCURA VERRILL. 437 



symmetry appears at practically the same time here as in 

 Podarke, and that there is as much differentiation in the ovum 

 as in any annelid with the unequal type of segmentation. The 

 theoretical bearings of this fact I shall discuss later. 



Table of Cleavages. 



I have followed all divisions up to about 140 cells ; later 

 than this only especial groups were followed. All of these 

 divisions are indicated in the accompanying tables. The well- 

 marked stages of the earlier cleavages are denoted by the num- 

 bers at the top of the column, but after eighty cells these 

 numbers must be regarded as only approximate. Each table 

 gives the divisions of a single quadrant and begins with the 

 4-cell stage. The direction of each division is indicated by 

 the straight line / inclined to the right for a dexiotropic, to the 

 left for a leiotropic, vertical for a meridional, and horizontal 

 for a horizontal cleavage. If it be remembered that the line 

 always has the direction of the boundary plane between the 

 two cells, I think the table will be readily understood. When 

 the products of a division are equal, that is indicated by the 

 sign of equality. If unequal, by the sign of inequality, placed 

 across the direction line. A plus (+) sign after a cell number 

 indicates that it has been seen to divide again, but its divisions 

 were not followed. 



In all cases the daughter-cells resulting from a division are 

 put in the column indicating the number of cells in the whole 

 embryo immediately after the division of these cells. Thus, 

 at the i6-cell stage, 2 A divides dexiotropically and unequally, 

 the larger cell lying below. At the completion of this divi- 

 sion the whole embryo contains twenty-four cells. The smaller 

 cell, 3a, does not divide again, until about forty cells, and 

 when this division is completed the whole embryo contains 

 fifty-six cells, etc. 



