Abstract
Measurements of Amblystoma punctatum and tigrinum have been made in order to secure data upon the normal rate of growth and upon the modifications of this growth rate by experimental procedure. Data show that the rate of enlargement during embryonic stages is dependent upon the temperature, the size at any named stage being correlated with the size of the egg. Length increase in the embryo is made at the expense of the other dimensions. The curve of absolute increments of length when plotted against time during embryonic development is S-shaped, terminating at the end of this period.
The mean lengths of Amblystoma punctatum, tigrinum, and Axolotls at this point of development are 15.61 mm., 14.07 mm., and 11.96 mm., respectively. Tables for mean length, standard deviation coefficient of variation, and the probable errors of these quantities demonstrate the value of the criterion used.
Growth following the embryonic period is dependent upon food—quality, quantity, and frequency of feeding. Where feeding is alike, size relations of the embryonic period hold for larval growth. No food has been found as adaptable for early use as the natural diet which consists of small aquatic forms. Beef-liver can be used at early stages and produces a remarkable acceleration of growth. Of the tissues tried, kidney is second in value.
In the later larval development and adult life, beef muscle produces greater growth than liver : at these stages, liver feeding is attended by excessive glandular production, by lack of growth, and often with loss of appetite. Death sometimes follows. There is a weakening of normal peristaltic action, which can be compensated for, partly at least, by use of agar. Beef muscle is of poor value for early larval growth and development.
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