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Loss of Weight in Starving Cassiopea

body-weight, days, calculated, table and cassiopeas

LOSS OF WEIGHT IN STARVING CASSIOPEA.

Eight freshly caught normal cassiopeas having different body-weights were subjected to starvation by placing them in filtered sea-water. The filtration was effected with all the precautions adopted by Mayer (1914) and the water (4,500 c.c.) in the vessel was changed once every day. The period of starvation was 21 days and the body-weights were taken every day for the first 6 days and then at 10 and 21 days. The loss of weight is shown in table 4.

These eight cassiopeas were divided into three groups composed of the three largest, the three medium, and the two smallest individuals respectively. The object of such grouping was to see whether or not the loss differed according to the size of the animal. Table 4 shows a distinct difference in the loss according to the initial body-weight. In general, the smaller cassiopeas lost relatively much more than did the larger (see table 5). This result agrees with the results found for the starving vertebrates. It is remarkable, however, that cassiopeas after losing nearly 62 to 80 per cent of their initial body-weight appear in no respect different from the normal cassiopea of similar body-weight. It is very difficult to distinguish the starved from the normal by merely looking at them unless the velar lobes happen to be turned upward— as occurs in some of the cassiopeas after several days of starvation.

Mayer (1914) found a simple law which governs the loss of weight in starving cassiopea. The law is represented by the following formula Y= W(1 where Y represents body-weight W after x days of starvation, and a stands for the constant that gives a fair measure of the rate of loss of weight. Mayer calls this constant a the coefficient of negative metabolism, since a increases as the loss of weight increases.

Extensive data given by Mayer show that this formula accords satisfactorily with his observed data. The starved cassiopeas in my

hands showed, however, a sharp drop in the body-weight within 24 hours after commencing starvation; thus the succeeding body-weights were altogether too low as compared with the calculated values, when this formula was applied. Assuming that the initial sudden loss in weight was due to some peculiar conditions not understood at present (possibly the escape of alive, etc.), I have taken the body-weight, 83.58 grams (see table 4), one day after starvation, as the starting-point, and computed the successive losses of weight according to the formulas Y = 83.58 Table 5 shows the observed losses of body-weights (from table 4) compared with those calculated by the revised formula.

Tama 5.

Observed Calculated Observed Calculated Dar,. Days.

body-weight. body-weight.

body-weight. body-weight.

grams.

grams. grams. MIMS.

1 83.58 83.58 5 63.66 68.08 2 77.85 79.40 6 58.19 64.68 3 72.49 75.43 10 52.36 52.68 4 67.74 71.66 21 29.97 29.97 By this modification the agreement between the observed and calculated values becomes much more satisfactory. The somewhat lower body-weight obtained in the present experiment as compared with that calculated was probably due to the frequent handling of the animal in order to determine the body-weight daily. The removal of the adherent moisture with filter paper previous to weighing is certainly severe treatment for the delicate medusan body. It is there fore rather a surprise to find that the formula, which has no additional provision for the various experimental conditions except the two fac tors (number of days and initial body-weights), can represent so closely the data here obtained.