490 JENNINGS— HEREDITY IN PROTOZOA. [April 24, 



and infected with the same bacteria as all the others. All are kept in watch- 

 glasses of the same form and size, close together in the same moist chamber. 

 Any characteristic differences in the resulting progeny must then be due to 

 conditions within the animal, and not to differences in the environment. If 

 we reach the same result, not merely in one experiment, but in a series con- 

 ducted in this manner, we can be sure of our results. 



Cultures of the five lines, D, c, g, i and E, prepared in the way 

 just described, were set in progress January 19, 1908. In order to 

 determine with certainty how much effect possible environmental 

 differences might have on the results (as well as for certain other 

 purposes), two lots each of D, g and i were used. If the two lots 

 of g, for example, show differences as great as those between g and 

 c, then, of course, we have no ground for considering g and c inher- 

 ently different ; the environmental differences account for all. These 

 lots were allowed to multiply till February 5. Then a sample of 

 each was killed and measured. Now a new lot of ten of each set 

 was prepared by the methods given above, and the animals were 

 again allowed to multiply till February 15, when samples were again 

 measured. 



It will be recalled that £ is a lot derived from ten specimens of possibly 

 diverse ancestry, from the culture 01, with an original mean length of 

 238.280 microns ; that the line D has shown in repeated determinations a 

 highest mean length of 202.280 microns (Table XVIII.) ; that c, g and i are 

 smaller lines, derived from single individuals ; g is known to be larger than 

 i, but the relation of c to these is unknown. 



The results of these breeding experiments are given in the fol- 

 lowing Table XXIV. 



The experimental results given in this table show certain things 

 clearly. 



I. The method of culture is adequate for bringing out the inher- 

 ent differences in different lines without confusion due to environ- 

 mental eft'ects. This is shown by the fact that when two cultures 

 are made from certain single lines, these show themselves after 

 breeding for many generations to be nearly identical, while the 

 different lines give diverse results. In only one case {D on Feb- 

 ruary 15) is there a notable difference btween the two samples of a 

 single line, but this is much less than the dift'erence between that line 

 and any other. 



