igoS] JENNINGS— HEREDITY IN PROTOZOA. 487 



differences, a single characteristic individual. This was done on 

 November 13. The specimen from the larget set I called g; it 

 measured approximately 130 to 140 microns in length. The speci- 

 men from the smialler set I called /; its length was about 90 to 95 

 microns. These two individuals were kept under the same condi- 

 tions and allowed to multiply. 



The small specimen i multiplied more rapidly than the large one 

 g. On November 16 there were but seven progeny of g, while i had 

 produced a large number. Two typical specimens of g were killed 

 and gave measurements of 160 X 48 microns and 164 X 56 microns. 

 Five typical specimens oi i ranged in size from 92 X 36 to 128 X 44 

 microns, with a mean of 103.2 X 39-2. 



Evidently, therefore, the progeny of ^ and / tend to retain the 

 dift'erences in size characteristic of the parents. The two lines were 

 kept for a long time, under the same conditions ; at intervals random 

 samples were measured. The measurements at different dates, with 

 the number of specimens on which they are based are given in 

 Table XXIII. , p. 488. TThe small numbers of specimens employed 

 on certain dates are due to the fact that only a small number ex- 

 isted at that time.) 



The great fluctuations in the dimensions of each line will of 

 course surprise no one who has examined that part of this paper 

 which deals with the effects of the environment. These fluctua- 

 tions are due mainly to differences in nutritional conditions. At 

 intervals it was necessary to add new culture fluid ; the dimensions 

 in both lines thereupon rose at once; they then gradually declined 

 till new fluid was added. Details on this matter are not necessary 

 for our present purpose. 



The important fact is, that in spite of all fluctuations, the lines g 

 and i retained throughout the three months in which they were 

 under observation their characteristic relative sizes. ^Multiplication 

 was probably at the rate of about one fission a day, so that the table 

 represents 90 to 100 generations. We have here two lasting races 

 comparable to the two races from our first culture, which we called 

 D and c. It is clear that neither g nor / is identical with D, since 

 the latter is much larger: whether either is the same as c we shall 

 inquire later. 



