,9o8.] JENNINGS— HEREDITY IN PROTOZOA. 459 



Yet, of course, these results are not produced haphazard ; what we 

 wish to study are the laws they follow. 



The eflfects of the environment were studied mainly on the same 

 animals that served for the study of growth. Two strains were 

 used; one consisted of descendants of the individual D, of the cau- 

 datum form, the other of descendants of c {aurelia form). The 

 results show the extent of the variations producible through environ- 

 mental action in the progeny of single individuals multiplying by 

 fission. No conjugation occurred in the D strain during the time it 

 was under experimentation. On a given date, therefore, the age of 

 the individuals, as measured in generations of the " cycle," was about 

 the same. 



Table XVIII. gives a summary of the statistical results in the 

 experiments on the effects of the environment ; it will be referred to 

 frequently in the following account (see next page). 



I. Progeny of D {caudatum Form). 



The individual D was isolated April 12, 1907; it measured, as 

 nearly as could be determined when alive, about 250 microns. It 

 was placed in culture fluid made of boiled hay and the progeny were 

 kept in such cultures for months. Characteristic progeny of D are 

 shown in Fig. 1, a to d. 



The experiments with the descendants of D may be divided inta 

 three series. 



First Series. 



Old Large Culture. — On June 11 a sample of 100 of the descend- 

 ants of D was killed, from a hay culture that had stood several weeks 

 and was flourishing, though multiplication was not occurring actively. 

 This culture was in a vessel about nine inches across. The measure- 

 ments of this sample are given in Table V. (page 406), while the 

 constants are found in row i, Table XVIII. 



Effects of Fresh Hay Infusion. — Three days after these measure- 

 ments were taken, a number of individuals of this culture were 

 removed and placed in a fresh hay infusion, in a watch-glass; in 

 this they were allowed to remain 24 hours. The increased food in 

 the fresh infusion caused them to increase much in breadth (from 

 49.000 microns to 64.880 microns), and at the same time to begin to 



