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yolk-cell divides soon after the formation of the mesoblast. This 
division is evidently confined to the nucleus and the immediately 
surrounding protoplasm, for no cell-boundary is seen between the two 
endoblast-nuclei (Fig. 9 E). Rarely lines are seen which apparently 
divide the yolk-cell, but that these are not cell-boundaries is shown 
by the frequent occurrence of both nuclei on the same side of the 
line. The two entoblast-nuclei remain in undivided for some time. 
In the later history of the mesoblast and entoblast my results 
agree in general with previous accounts. 
One polar body persists until a late stage, and gives a basis for 
orientation. I have not studied the maturation-phases, but according 
to previous accounts this persistent polar body is the second one. 
The history of the persisting polar body is interesting, and since it 
offers a means of orientation not hitherto employed in the study of 
Cirripede ova, a brief account of its history is here given. In the 
4-cell stage the body is seen near the intersection of the cleavage- 
planes lying deep in the first furrow (Fig. 3). In the formation of 
the 8-cell stage it is crowded down deeper into the furrow, and by 
the shifting of one cell it usually becomes covered. In the 16 cell 
stage it is always found in the yolk-mass beneath the blastoderm, 
but still it remains near the original position on the exterior (Fig. 7). 
It is found here often in the 32- and 64-cell stages, but it appears 
to be disintegrating, and in later stages disappears. Examination of 
hundreds of eggs shows that the above described process is normal. 
Summary. 
The ectoblast is separated from the mesentoblast by four divisions. 
The four blastomeres thus formed repeadly divide and grow around 
the yolk-cell in an epibolic fashion. The divisions of these blasto- 
meres are in every normal stage approximately synchronous with the 
division of the yolk-cell. Thus stages of 2,4, 8, 16 and 32 cells are 
formed. The successive cleavages occur in a definite and regular 
order. The blastomeres are not cut off from the yolk in variable and 
indefinite positions, but, as has been pointed out, they are arranged 
symmetrically with respect to the median plane. In all important 
respects the cleavage of L.fascicularis is as regular as is ordinarily 
found in other Metazoa. 
All previous observers have failed to recognize any definite order 
in the cleavage of Cirripede ova. It has always been described as 
exceedingly variable, irregular and sui generis. There is undoub- 
tedly some irregularity and variation in the cleavage of the ova of 
