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earlier observers to the conclusion that all the ectoblast was separated 
from the yolk in a single cell which by repeated division produced 
the blastoderm. The cleavage plane which begins in A is soon con- 
tinued through the yolk-cell, dividing it into two almost. equal cells 
(Fig. 3). The greater part of the yolk is concentrated in the cell 
which lies most posteriorly. Viewed from the animal pole, with the 
yolk-cell toward the observer, the second ectomere (BD) is always 
formed to the right of the yolk-cell. Some time intervenes between 
the completion of the nuclear division and the formation of a cell-wall 
between the second ectomere and the yolk-cell. Such a condition 
evidently suggested the term “merocytes”, which Groom applied to 
these nuclei with the surrounding protoplasm. In this and succeeding 
formations of ectomeres from the yolk-cell there are exhibited no 
phenomena which seem to justify the term “emerging merocytes”, 
which the above mentioned author has used to describe the formation 
of new ectoblastic segments. The early divisions of the yolk-cell are 
so nearly equal that neither of the resulting cells can be said to 
“emerge”. The so called “merocytes” do not exist in L. fascicularis, 
‚at least, except as transitory phases of division. The ectomeres are 
formed from the yolk-cell by ordinary division which is not at all 
different from the later divisions of the previously formed ectomeres. 
The term “merocyte” is in this Cirripede, at least, unnecessary and 
misleading. 
In the four-cell and later stages many of the cells often become 
shifted after division from their original position. The different arrange- 
ments of cells which are so commonly found are not due, as a rule, 
to variations in the order of division. The cells in the vast majority 
of cases are formed in definite positions and in a quite constant order. 
The third cleavage usually takes place in the ectoblast-cells A, 
A’ and B somewhat earlier than in the yolk-cell, but sometimes all 
the cells are found in the same phase of division (Fig. 4). The planes 
of this division are in the ectoblasts inclined 60 to 90 degrees to 
those of the previous cleavages. The third ectomere C is formed on 
the left of the yolk-cell (Fig. 5). The division is almost equal in all 
the cells; but in any stage after the 4-cell stage the yolk-cell appears 
very much larger than the other cells. During the progress of the 
segmentation, the yolk-cell does not appear to diminish greatly in 
size, although it is almost equally divided several times. This fact 
evidently had much weight in leading the earlier observers to the 
conclusion that the ectoblast was separated from the yolk-cell by one 
and only one division. Sections show that this apparent constancy 
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