BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
GENERAL SUMMARY. 
A. Observations. 
l. Many divisions take place during the cleavage of Asplanchna in 
which the spindle lies in the shortest axis of the cell, in the direction of 
greatest. pressure, and the ensuing division results in the production of 
contact surfaces of greatest area. 
2. In the cleavage of the ectoderm of Asplanchna any cell of any one 
quadrant cleaves in the same direction as the corresponding cell of the 
other quadrants, though the forms of the corresponding cells may vary 
excessively. Conversely, cells of the same form and with similar relations 
to surrounding cells, but belonging to different layers or series, may 
divide with spindles in exactly opposite directions. 
3. The entodermal cell follows the same rhythm and direction of 
cleavage as the other cells, so long as it remains on the exterior and thus 
corresponds in position with other cells of the ege. When it becomes 
enveloped by the other cells, so as to come into different relations with 
the axis of the embryo, its plan of cleavage changes, showing no definite 
relation to that of the ectoderm. 
4. All the cleavages in the ectoderm are to a late period either 
equatorial or meridional, so that the position of any given spindle is 
either parallel or perpendicular to that of the preceding spindle. 
5. There is no regular alternation in the direction of spindles. Equa- 
torial cleavages may follow successively for three or more generations, 
and the same is true of meridional cleavages. 
6. The position occupied by the two asters after they have passed to 
opposite sides of the nucleus does not indicate the direction of the 
ensuing spindle. "lhis may oceupy the position indicated by the asters, 
or the definitive position may be gained by a rotation of the asters and 
nucleus at the passage into the karyokinetie condition. 
7. There is no “regular angle of rotation ” (Heidenhain) in a mechani- 
cal sense, since (a) in cells of different layers, in one case the augle may 
be zero, in the other ease 90 degrees; and (b) even in cells where tho 
direction of the previous spindle and the direction of the following spindle 
are the same, the asters may move in an entirely different manner. In 
one cell the rotation may be directly through an angle of 90 degrees, 
and in a single plane, while in another there may be complex movements 
and rotation successively in different planos. 
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