JEXXIXGS: DEVELOPMENT OF ASPLANCHNA HERRICKII. 107 



8. The position aud movements of the asters in the resting stage seera 

 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, aud 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 ai-e 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 

 ceU passes into the karyokinetic condition it becomes more rounded, 

 the cytoplasm tends to gr'oup itself symmetrically about the spindle, and 

 the cell elongates in the direction of the spindle. 



14. The spindle genei-ally (not always) lies in either the longest or 

 the shortest axis of the cell, as maintained by Eoux. 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 the 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 cleavage progresses the 

 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 



