536 H. S. Jennings and George T. Hargitt. 



records existed for several different lines for each race, there were 

 chosen: (1) the lines that were healthy, not showing frequent 

 deaths during the experiment, (2) the lines in which the fission 

 was most nearly uniform in rate. 



A number of important points are brought out by the table. 



1. There are differences in the rate of fission between different 

 lines belonging to the same race, and thus derived originally from 

 the same individual. Thus, in the race La, the lines derived from 

 the individual a show during every week, as well as for the entire 

 period together, a more rapid rate of fission than the lines derived 

 from the individual h. This inherited differentiation within pure 

 lines is of the greatest interest; it will be dealt with in a sepa- 

 rate paper. 



2. Within the same line the rate is sometimes very different 

 for a certain period, as a week or ten days, from the rate during 

 the rest of the time. This is much more evident when one in- 

 spects a table in which the fissions are recorded day by day. The 

 rate in a given line is th^re seen at times to drop, remain low for 

 perhaps ten days, then return to the original rate. In most or all 

 of these cases there are evidences of pathological conditions dur- 

 ing these periods of lowered rate of fission. Monstrosities appear, 

 and many of the specimens die. Therefore these periods of slower 

 rate are not to be considered as giving the characteristic rate for 

 the race when healthy. In comparing different races, the periods 

 when the rate of fission is high and uniform should be compared. 

 (The influences determining these lasting changes in the rate of 

 fission will be dealt with elsewhere.) 



3. More important for our present purposes is the fact that in 

 spite of the fluctuation within a given race, it is evident that 

 there are marked characteristic differences in rate of fission between 

 different races. In the aureha group there are evidently three 

 different sets, so far as rate of fission is concerned. The race k 

 multiphes at about the same rate as do the characteristic lines of 

 the caudatum group, having as a rule ten to twelve fissions per 

 week, and in the total period of thirty-seven days, from fifty- 



