TEMPERATURE AND LIGHT AS FACTORS INFLUENCING THE RATE OF SWIMMING OF LARVÆ OF THE MUSSEL CRAB, PINNOTHERES MACULATUS SAY

¹ From the Zoölogical Laboratory, Harvard University, and the Woods Hole Oceanographic Institution

1. Larvæ of Pinnotheres maculatus Say are shown to be satisfactory animals for the study of photokinesis. The velocity of swimming is found to be greatly influenced by temperature and light intensity. Age, although not carefully investigated at present, is also an important contributing factor in determining the rate of locomotion.

2. A series of measurements of the effect of temperature on the velocity of swimming, at a constant light intensity, showed the applicability of the Arrhenius equation, and yielded values of µof 12,800 above 18.5° and 16,900 below 18.5° C.

3. The larvæ are found to be sensitive to only a small range of light intensities. At temperatures between 20-25° C., the maximum possible velocity of swimming is attained at intensities between 10 to 25 meter candles. When velocity is plotted against light intensity a smooth curve is obtained. The same data when treated empirically according to the equation log V = k log I – C, yields essentially rectilinear graphs which are more satisfactory for a comparison of such data.

4. When series of measurements are made to determine the effect of light at different constant temperatures it is found that, besides a marked effect on general activity, there is a change in the relationship of velocity to intensity; the slopes of the curves change, and the maximum possible velocity of swimming for each temperature is reached earlier at the higher temperatures.