. Biological lectures delivered at the Marine Biological Laboratory of Wood's Holl [sic]. Biology. 114 BIOLOGICAL Fig. I. — Left side of fertilized unsegmented egg of Amphitrite. Polar globules indicate the position of the animal pole. is the transverse ciliated fringe, the prototrocJi (Figs. 13-16), and it is the purpose of this paper to bring together and compare the observations of several workers who have employed the method of cell- lineage to determine the exact origin of this organ. In order to establish a con- crete example for comparison, let us proceed at once to the accou
. Biological lectures delivered at the Marine Biological Laboratory of Wood's Holl [sic]. Biology. 114 BIOLOGICAL Fig. I. — Left side of fertilized unsegmented egg of Amphitrite. Polar globules indicate the position of the animal pole. is the transverse ciliated fringe, the prototrocJi (Figs. 13-16), and it is the purpose of this paper to bring together and compare the observations of several workers who have employed the method of cell- lineage to determine the exact origin of this organ. In order to establish a con- crete example for comparison, let us proceed at once to the account of the origin of a simple and fairly typical pro- totroch, namely, that of the marine annelid AmpJiitrite. The spherical &^'g is of medium size, about one-tenth of a millimeter in diameter, without much yolk, and is unprotected save by a thin wrinkled Q%% membrane. Fig. I represents the &g^ seen from the left side. Fertilization has taken place, and the polar globules remain attached. The succeeding figures represent the q^^ in the same position, unless otherwise stated. Fertiliza- tion takes place in the sea water, and the cleavage pro- gresses so rapidly that the larva swims in a few hours. The first cleavage being un- equal, the 2-cell stage is char- acterized by the possession of a larger and a smaller blastomere, which are represented in side view in Fig. 2. After this the cells divide with some irrregularity in time and in the. 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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