. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 240 TREADWELL. from the ordinary pigment of the rest of the cell, but containing granules of a faint yellow color, agreeing in this respect exactly with the prototroch band of the normal trochopore. In this embryo there is, then, not merely a differentiation—without cleav- age—of cilia, but of the charac- o teristic protoplasm accompanying these cilia—or, in other words, we have here, in the unsegmented embryo, not merely a differentia- tion of cilia, but a differentiation of prototrocli cilia. Later, fused masses like those
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 240 TREADWELL. from the ordinary pigment of the rest of the cell, but containing granules of a faint yellow color, agreeing in this respect exactly with the prototroch band of the normal trochopore. In this embryo there is, then, not merely a differentiation—without cleav- age—of cilia, but of the charac- o teristic protoplasm accompanying these cilia—or, in other words, we have here, in the unsegmented embryo, not merely a differentia- tion of cilia, but a differentiation of prototrocli cilia. Later, fused masses like those just described are apt to break down, setting free the ciliated fragments, and by the twentieth hour the culture will be swarming with ciliated fragments derived from this source and from the breaking away of the " dwarf' described above. These, of course, have not even a superficial resemblance to nor- mal embryos. Fusion phenomena are rare in Podarke as compared with Cluetoptcrits, the largest fused masses I have found containing. 1 IG. 12. Unsegmented embryo formed by fusion with well-differen- tiated band of cilia. Living material. not more than six eggs. SUMMARY. 1. After treatment with 2 }•< nKCl solution, eggs of Podarke obscitra exhibit various cleavages and pseudo-cleavages. 2. The pseudo-cleavages involve only the cytoplasm and not the nucleus, and have no resemblance to the normal cleavages. 3. The cleavage involves both nucleus and cytoplasm, and may give rise to a ciliated embryo. The cleavage in this case, however, does not resemble the normal. 4. Ciliated embryos may arise without cleavage. The differ- entiation may be carried very far in such cases. This is espe- cially noticeable in the character of arrangement of cilia. 5. Fusion of embryos may occur, but in the solution men- tioned, much fewer cells unite than in, r. g., CJicstoptcrns. MARINE BIOLOGICAL LABORATORY, WOODS HOLE, MASS., Sept. 5, Please note that these images are extracted
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