94 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
tion is carried to the equator of the egg. The polar cell itself is shifted 
at tho same time, and it seems possible that during this rapid rotation 
it may be transferred to a region of the egg different from its original 
position. Such shiftings of the polar cell, though to a less extent, 
are mentioned by Zelinka (pp. 55, 58). During the “sehr schnell ver- 
laufendes Phänomen” of the rotation of the egg within its shell, the 
relatively different shifting of the polar cell might have been over- 
looked. This is, however, only the suggestion of a possibility, for which 
there is no direct evidence in Zelinka's work. 
It is to be noted that in the above discussion I have employed 
throughout the orientation of the egg used by Zelinka, and not that 
adopted in my own account of the development. 
D. CLEAVAGE. 
The first cleavage in the two species of Asplanchna differs from that 
of Callidina russoola in being exactly transverse to the long axis of the 
egg. In the latter form, according to Zelinka, the first cleavage plane 
is oblique to the spindle, and the spindle itself is oblique to the long 
axis of tho egg. By a change of their relative positions immediately 
after division, the two cells are later brought into the same position 
relative to each other as in Asplanchna, and even at first the cleavage 
plane in the two forms oceupies the same position relative to the place of 
polar-cell formation. The difference thus is of little importance, except 
that, from a cyto-mechanical standpoint, it shows that the form of the 
ege does not determine the position of the first cleavage spindle. In 
Eosphora also (Tessin, '86) the first cleavage plane is oblique to the 
g, whereas in Melicerta ringens (Zelinka, '01) and 
Asplanchna Sieboldii (Lameere, ’90) the first cleavage plane is transverse 
to the long axis, as in Asplanchna Herrickii and Asplanchna priodonta. 
The second and third cleavages in the two species of Asplanchna 
(Plate 1, Fig. 6, Plate 2, Figs. 8-16) are essentially similar to the 
corresponding cleavages of Callidina and of other rotifers in which 
the development has been described. For convenience in compar- 
ing the later stages, I give hero a table showing the correspond- 
long axis of the eg 
ence between the cells of Asplanchna in the eight-cell stage and those 
of Callidina. 
Asplanchna. Callidina (Zelinka, ’91). Asplanchna. Callidina (Zelinka, ’91). 
aus Sed IPIS SUA dL O04 Kae ax b EAM. 
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