. Biological lectures delivered at the Marine Biological Laboratory of Wood's Holl [sic]. Biology. Fig. I. —Amphitrite, four-cell stage. Fig. 2. —Podarke, four-cell stage. the first division is unequal, and this difference in size is con- tinued into the four-cell stage (Fig. i).^ Here one cell is very much larger than either of the other three, and lies at what will be the posterior end of the future embryo. Notice here that the second plane of cleavage is not a straight line, but it cuts the first in two points some distance apart. The portion of the second furrow between these two points is
. Biological lectures delivered at the Marine Biological Laboratory of Wood's Holl [sic]. Biology. Fig. I. —Amphitrite, four-cell stage. Fig. 2. —Podarke, four-cell stage. the first division is unequal, and this difference in size is con- tinued into the four-cell stage (Fig. i).^ Here one cell is very much larger than either of the other three, and lies at what will be the posterior end of the future embryo. Notice here that the second plane of cleavage is not a straight line, but it cuts the first in two points some distance apart. The portion of the second furrow between these two points is the so-called " cross furrow," or " ; I shall follow Conklin in calling it the " polar ; It is obviously formed by the rotation of cells A and C to the left, so that they lie partly over B and D. In Amphitrite, as in other 1 Mead, " Development of Marine Annelids,"/<?2/r«. of Morph., vol. xiii. 2 I have modified slightly the lettering in the figures taken from Mead to corre- spond with a nomenclature proposed for Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Marine Biological Laboratory (Woods Hole, Mass. ). Boston, Ginn & Co
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