_ now much smaller than it was and has no nucleolus, while in the 
58 The American Naturalist. [January, 
The author thinks that the difference in opinion between Claus and — 
Goette is partially due to there being two kinds of cells that find t 
way into the cleavage cavity. Besides the large cells just deseri 
he found in a much smaller number of cases one or two very sm 
cells that look precisely like the small cells that appear in the deep 
part of the ectoblast at about the time gastrulation begins. 
There is no evidence that the immigrating cells have anything to 
with the formation of the entoblast, and Goette’s case is further weak- 
ened by the fact that all the conditions shown in his figures (6-9) 
easily be reproduced from sections of invaginating gastrule of 
single stage of development. 
Cleavage in Aequoria Forskalea.—Dr. V. Hecker’ contri 
utes an interesting series of observations on this subject. He fim 
that when the specimens are in good condition the time relatio 
between the successive periods of activity are remarkably precise. 
If ripe, the eggs are laid between 7 and 7.30 A. M. The first polar 
body is extruded at 9 A. M. The entrance of the spermatozoan and 
the division to form the second polar nucleus takes place at 9.30. 
10 A. M. the dyaster stage of the first cleavage nucleus occurs, 
with it the first indication of the division of the cell body. 4 
daughter nuclei are undergoing metakinesis at 11, and at 12 the four 
nuclei of the next set are in the dyaster stage. The nuclear divisions 
continue to take place an hour apart at least as far as the sixty-four — 
cell stage, and this seems to show that the nucleus is not affected 
this period by the amount of cell protoplasm that it controls. 4 
mally nuclear division takes place at the same time throughout i 
egg, and the blastomeres are of equal size up to the sixty-four-cell sta 
When eggs are laid after the specimen has been kept in an aquari 
several days, irregularities generally occur in the time of nuclear 
ion and in the size of the blastomeres. At the same time a path 
ical form of nuclear division, the triaster, appears, and the mas 
cells loses its spherical shape. 
A remarkable feature of the cleavage of the egg of Aequoria 
presence of a body for which the author proposes the name Me 
eleolus. In the older ovarian eggs and in eggs just laid there 18 ® 
large nucleus containing a very fine network of chromatin and àla! 
~ spherical or renifurm nucleolus. About half an hour after the egg 
_ laid this nucleolus appears to have been extruded, for the nucleus 
"Archiv. fur Mikro. Anat., 40 Bd., 2 Heft. 
