DEVELOPMENT OF THE EGG OF THE MACKEREL AT DIFFERENT CONSTANT TEMPERATURES.

1. Mackerel egg development was followed to hatching at constant temperatures of 10 degrees , 11 degrees , 12 degrees , 13 degrees , 14 degrees , 15 degrees , 16 degrees , 17 degrees , 18 degrees , 19 degrees , 20 degrees , 21 degrees , 22 degrees , and 24 degrees C. Experiment showed that typical development could be realized only between 11 degrees and 21 degrees . 2. The length of the developmental period increases from 49.5 hours to 207 hours when the temperature is lowered from 21 degrees to 10 degrees C. 3. The calculated micro for the development of the mackerel egg is about 19,000 at temperatures above 15 degrees and approximately 24,900 for temperatures below 15 degrees C. 15 degrees is, apparently, a critical temperature for this process. 4. The calculated values of micro for eight stages of development preceding hatching, i.e. 6 somites, 12 somites, 18 somites, 24 somites, three-quarters circles, four-fifths circles, five-sixths circles, and full circles, are essentially the same as the micro's for hatching, indicating that the rate of differentiation up to hatching is governed by one process throughout. Critical temperatures for these stages approximate 15 degrees . 5. The total mortality during the incubation period was least at 16 degrees C. where it amounted to 43 per cent. At temperatures above and below this there was a steady increase in the percentage of mortality which reached 100 per cent at 10 degrees and 21 degrees .