. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 154 C. LADD PROSSER It was much easier to observe the hearts during the early period when the carapace was soft and fairly transparent. At the age of about four weeks pigment developed, the carapace hardened, and the heart could not be seen easily. It was found that in the older embryos a small area behind the median eye remained fairly translucent and light reflected from the anterior end of the heart could be observed there. After about 30 days of development the heart rates became somewhat more irregular. LIMULUS EMBRYOS.
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 154 C. LADD PROSSER It was much easier to observe the hearts during the early period when the carapace was soft and fairly transparent. At the age of about four weeks pigment developed, the carapace hardened, and the heart could not be seen easily. It was found that in the older embryos a small area behind the median eye remained fairly translucent and light reflected from the anterior end of the heart could be observed there. After about 30 days of development the heart rates became somewhat more irregular. LIMULUS EMBRYOS. FIVE MINUTE INTERVALS FIG. 3. Effect of acetylcholine and eserine on hearts of two Limulus embryos^ Embryo A at 22, 32, and 38 days of development and embryo B at 28 and 36 days. Data were obtained on 11 embryos. In two of these the period of observation extended over only four days but in the others data were obtained for periods between seven and 19 days. Typical curves are shown in Figure 3 and the entire experiment summarized in Table I. During the myogenic period acetylcholine had no effect upon the hearts of the Limulus embryos. Specimens were kept in concentrations of 10~4 for periods up to one hour. Eserine 10~4 was applied either with the acetylcholine or prior to treatment with it and still there was no effect of the acetylcholine. On the twenty-eighth to thirtieth days when, according to Carlson, the heart ganglion is present there was still little or no action. On the thirty-first day, however, two embryos showed acceleration and by the thirty-fifth day most of the specimens were accelerated by acetylcholine as is the adult heart. Only when 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. ); Marine Biological Laboratory (Woods Hole, Mass. ). An
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