. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 82 J. B. JOHNSTON. into the ventral vessel very much as the valves in the parietals project into the dorsal. Thus, with the valves in the dorsal be- tween each two pairs of hearts and the four valves in each heart, regurgitation of blood during the strong cardiac contractions is effectively guarded against. The study of the fine structure of the valves has presented great difficulties because methods of fixation which give satisfac-. FIG. 3. A diagrammatic cross-section through one of the hearts to show the posi- tion
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 82 J. B. JOHNSTON. into the ventral vessel very much as the valves in the parietals project into the dorsal. Thus, with the valves in the dorsal be- tween each two pairs of hearts and the four valves in each heart, regurgitation of blood during the strong cardiac contractions is effectively guarded against. The study of the fine structure of the valves has presented great difficulties because methods of fixation which give satisfac-. FIG. 3. A diagrammatic cross-section through one of the hearts to show the posi- tion of the valves. The chloragogue and peritoneal epithelium are not drawn. tory preparations of all other tissues give very imperfect pictures of these valves. This itself indicates one fact regarding their structure, namely, that they are composed of very soft-bodied or watery cells which may appear vacuolated or shrunken, or even macerated. In many preparations the valves appear only as masses of granular or coagulated material containing many ovoid nuclei. In the most successful sections, however, the valves. 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. ); Marine Biological Laboratory (Woods Hole, Mass. ). Annual report 1907/08-1952; Lillie, Frank Rattray, 1870-1947; Moore, Carl Richard, 1892-; Redfield, Alfred Clarence, 1890-1983. Woods Hole, Mass. : Marine Biological Laboratory
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