. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. GROWTH OF ARMS IN ARBACIA PLUTEI 35 microns) proved quite variable. The data therefore are averages based on selection of the better developed specimens. Since nutrition markedly affects arm lengths, especially in plutei older than 4 days (Harvey, , table, p. 294) we can assume that selection influences the uniformity of the measured material by segregating comparable samples of the best fed individuals. Developmental time, recorded in days, weeks, or months, and now reduced to days, does not include pre-pluteal time. Th
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. GROWTH OF ARMS IN ARBACIA PLUTEI 35 microns) proved quite variable. The data therefore are averages based on selection of the better developed specimens. Since nutrition markedly affects arm lengths, especially in plutei older than 4 days (Harvey, , table, p. 294) we can assume that selection influences the uniformity of the measured material by segregating comparable samples of the best fed individuals. Developmental time, recorded in days, weeks, or months, and now reduced to days, does not include pre-pluteal time. This introduces an error in timing, but the error is reasonably constant and if corrected, would only improve the distribu- tion of the points. These are plotted in Figure 1 according to the modified allo- metric equation. Log Microns .7 —. FIGURE 1. Modified allometric plot of growth in length of anal arms in the pluteus of Arbacia punctulata. Original data of Ethel Browne Harvey. As the figure shows, arm lengths for the first and twenty-first days are less than the equation demands while those of the 7th, llth and 14th days are greater. Since the 14th and 21st days fluctuate about the line, we can attribute these two deviations to chance. Whether the 7th and llth days represent systematic deviations may be an open question. Certainly the remaining points closely approximate the pre- dicted straight line. It would be curious if this approximation were attributable to the accidents of a selection involving judgement and made for other purposes. Thus in spite of criticisms some of which may be valid, the modified allometric equa- tion seems to apply to a wide range of growth measurements. LITERATURE CITED GLASER, O., 1938. Growth, time and form. Biol. Rev., 13: 20-58. HARVEY, E. B., 1949. The growth and metamorphosis of the Arbacia punctulata pluteus and late development of the white halves from centrifuged eggs. Biol. Bull., 97 : 287-299. HUXLEY, J. S., 1932. Problems of Re
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