JENNINGS: DEVELOPMENT OF ASPLANCHNA HERRICKII. 107 
8. The position and movements of the asters in the resting stage seem 
partly determined by the form of the cell. 
9. The rotation of the nucleus and asters into the definitive position 
at the time of karyokinesis often takes place from the longer into the 
shorter axis of the cell, and apparently from the direction of least pressure 
into the direction of greatest pressure. 
10. The form of the cells in many cases does not conform to the law 
of minimal surfaces, being (a) changeable, and (b) even in the resting 
stage widely at variance with the conditions required by the law. 
11. Many of the cleavages are unequal, sometimes extremely so, but 
the inequality shows no significant relation to accumulations of yolk 
material. (See 16.) 
12. The sequence of cleavage is (within very narrow limits of varia- 
tion) constant, and shows no relation to accumulations of yolk, There 
is a general tendency for larger cells to divide faster, but not all the 
facts regarding the succession of cleavages show relation to the com- 
parative size of the cells. 
13. In the resting stage the cells seem to be passive, taking what- 
ever form is impressed upon them by the surrounding cells, As the 
cell passes into the karyokinetio condition it becomes more rounded, 
the cytoplasm tends to group itself symmetrically about the spindle, and 
the cell elongates in the direction of the spindle. 
14. The spindle generally (not always) lies in either the longest or 
the shortest axis of the cell, as maintained by Roux. But apparently 
this is due in Asplanchna to the fact that the cytoplasm tends to group 
itself symmetrically about the spindle. 
15. A change of the relation of a cell to the axes of the egg, as by a 
displacement due to the other cells, results in a change of the position of 
the spindle with reference to the axes of the egg. 
16. During cleavage a cloud of granules is segregated in a portion of 
the cell which is to form the entoderm ; this mass passes from thé an- 
terior and ventral side of the entoderm cell to its posterior and dorsal 
side, and is there separated off at the seventh cleavage into the smaller 
entodermal cell. 
17. The egg retains its ellipsoidal form throughout all the processes 
of development, up to a late stage, though as oleavage progresses tho 
blastomeres shift extensively their positions with relation to this form. 
This retention of the ellipsoidal form by the egg cannot be referred to 
any simple mechanical factor. (See pages 81, 82.) 
18. Gastrulation accompanies cleavage, and advances step by step 
