The Influence of Environment 299 



If we assume that the temperature coefficient for 

 the segmentation of the egg is that of a chemical re- 

 action (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 influ- 

 ence of temperature upon the organism is so constant 

 that if disturbing factors are removed it would be pos- 

 sible 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. 



Facts of this character should dispose of the idea 

 that the organism as a whole does not react with that 

 degree of machine-like precision which we find in the 

 realm of physics and chemistry. Such an idea could 

 only arise from the fact that biologists have not been 

 in the habit of looking for quantitative laws, chiefly, 

 perhaps, because the difficulties due to disturbing 

 secondary factors were too great. The worker in 

 physics knows that in order to discover the laws of a 



