--------------+------------------------------ | TEMPERATURE COEFFICIENT OF +-------------+---------------- _Temperature | _Latitude | Interval_ | of | _Segmentation_ | Variation_ | --------------+-------------+---------------- °C. | | 9-19 | 4.2 | 4.7 10-20 | 3.9 | 3.8 11-21 | 3.2 | 3.3 12-22 | 2.8 | 3.1 13-23 | 2.4 | 2.8 14-24 | 2.3 | 2.8 15-25 | 2.6 | 2.5 --------------+-------------+---------------- If we assume that the temperature coefficient for the segmentation of the egg is that of a chemical reaction (other than oxidation) underlying the process of segmentation, the fluctuating variation in the time of the segmentations of the various eggs fertilized at the same time is due to the fact that the mass of the enzyme controlling that reaction varies within definite limits in different eggs. The first egg segmenting at a given temperature has the maximal, the last egg segmenting has the minimal mass of enzyme. It should be added that the time of the first segmentation is determined by the cytoplasm and is not a Mendelian character, as was stated in a previous chapter. 3. The point of importance to us is that the influence of temperature upon the organism is so constant that if disturbing factors are removed it would be possible to use the time from insemination to the first segmentation of an egg of _Arbacia_ as a thermometer on the basis of the table on page 295.