562 JACQUES LOEB AND MARY M. CHAMBERLAIN 



m, which at t° divide after 113' will divide at (t — 10)° after 

 Qio X 113 minutes, since the temperature coefficient must be 

 the same for both types of eggs. If we call the difference in the 

 time of segmentation between the slowest and fastest egg the 

 latitude of variation, this latitude of variation should vary in 

 direct proportion to the temperature coefficient for cell divi- 

 sion if our theory is correct. 



Ill 



We will first give the temperature coefficient of cell division 

 for the egg of Arbacia for different temperatures; i.e;, the results 

 of measurement of the time required from the moment of insemi- 

 nation to the moment when the first egg in the field was seen to 

 divide. The eggs had been kept in a water bath with constant 

 temperature, and a little before the cell division was expected 

 to occur (which time we knew from the former observations of 

 Loeb and Wasteneys) the eggs were put into a watch glass of 

 the temperature of the eggs and the exact time ascertained when 

 the first egg of the lot underwent cell division. Table 1 gives 

 these times according to Loeb and Wasteneys, and according 

 to our own observations. The reader will notice how closely 

 both values agree. ^ Our values are the average of a number of 

 determinations, which show only a negligible variation. 



Beyond 31° no segmentation occurs. We tried no experi- 

 ments on the latitude of variation beyond 25° or below 9°, since 

 outside of these limits the segmentation is no longer entirely 

 normal. 



From the results of table 1 we compute the temperature co- 

 efficients for the time from insemination to the first appearance 

 of cell division (table 2). 



In order to determine the latitude of variation of the time 

 of segmentation — i.e., the interval between the time at which 

 the first egg of a set begins to segment and the time when the 

 last egg segments for a certain temperature, we proceeded as 



* The eggs were always used in the first hours after they had been removed 

 from the animal. The time required for the first cell division was remarkably 

 constant in different experiments. It is worth mentioning that such constancy 

 is only possible when the temperature is kept constant. 



