98 BULLETIN: MUSEUM OF COMPARATIVE ZOÖLOGY, 
being the same as in the other three quadrants (see Figs. 33 and 37). 
In Asplanchna, moreover, the fifth cleavage in the other quadrants is 
well advanced before any of the divisions for the sixth cleavage in 
quadrant D have taken place. 
Zelinka does not follow the cleavage in the other three quadrants cell 
by cell. He states that the dorsal cells of these quadrants (all?) are 
divided by planes parallel to the long axis of the egg, as is the case for 
all but the fourth or most dorsal layer in Asplanchna, and that the 
ventral cells a, 05", and c (47, bj, and II, Zelinka) are the last to 
divide. In Asplanchna, as shown in Figures 39-44 (Plates 5 and 6), 
all the cells of these quadrants divide meridionally except those of the 
dorsal layer, which divide equatorially. 
It is obviously impossible to compare in detail the cleavage in the two 
forms at this time, or to reduce the condition described for Callidina to 
the regular scheme of cleavage exhibited in Asplanchna. Certain facts 
are perhaps worthy of notice, as showing the possibility that the cleavage 
in Callidina is not so different from that of Asplanchna as would be 
inferred from what is indicated above. The relation of the cells in 
quadrant D are somewhat similar in Figures 30 and 34 of Zelinku's 
work to a later condition in Asplanchna, — a condition reached, how- 
ever, in a very different way, and shown in Figures 58 (Plate 7) and 66 
(Plate 8). Further, the unequal cleavages of this quadrant are very 
confusing, and easily overlooked. Zelinka's work was apparently done 
almost entirely on living material, which does not lend itself as well as 
does preserved material to precise orientation of the object, and to its 
y as to permit views from all directions. It was 
only by bringing together a complete series, in which the k: 
rotation in such a 
-yokinetic 
process in was represented in various stages by several 
3 3 able to determine absolutely the course of events 
Specimens, 
unequal division of the cell dë! is especially 
did not observe it till the break in the rhythm 
this point set me at work upon a minute study of a series 
of cleavag: 
of eggs separated in avage conditions by very short intervals only. 
It i: 
cleavage to occur, Zolinka figures (Taf. II. Fig. 31) a small vesicle lying 
worth noting that in Callidina, shortly after the time for this 
almost exactly in the place occupied by the minute vesicle given off at 
this cleavage in Asplanchna, viz. between the ventral cells of quadrants 
A and B (a, and b, Zelinl 
J Zelinka considers this to be the polar 
cell, although at a previous stage he had observed that the polar cell 
had become displaced and now lay "arther dorsad, on the outer surface 
