464 JENNINGS— HEREDITY IN PROTOZOA. [April 24, 



microns, and the variability in length almost doubles, increasing from 

 7.794 to 13.262. Owing to the inclusion of many young individuals, 

 in which the length is increasing while the breadth is stationary or 

 decreasing, the correlation between length and breadth decreases to 

 .3945. Inspection of Tables VI. and VII. (page 412) shows at 

 a glance the great effect of nutrition and division on the range and 

 distribution of variations in size and form. 



Injurious Bacteria.— A remarkable effect of what may be called 

 " bad " conditions is shown in this series of experiments. The same 

 watch-glass culture shown in row 3, Table XVIII., was allowed to 

 stand for a week, till June 25. Bacteria of a certain character mul- 

 tiplied greatly, and seemed to get the upper hand of the Paramecia. 

 The latter became opaque and abnormal in appearance, and some of 

 them died, disintegrating into shapeless masses. It was now observed 

 that many of the specimens still living were very large, and that 

 variation in size was extreme. The distribution of the variations is 

 shown in Table LII. ; the constants in row 5, Table XVIII. Though 

 no multiplication is occurring, so that no young are present, the 

 range of variation is from 140 to 256 microns, while in row 3, from 

 which this lot is derived, the range is only from 148 to 212 microns. 

 The mean length has increased to 201.888 microns, one of the greatest 

 mean lengths ever observed in progeny of D. The maximum size 

 for descendants of D was likewise reached in this culture; in no 

 other case were specimens 256 microns long observed. 



Starvation. — In striking contrast with the effects of much nutri- 

 tion (row 4, Table XVIII.) and of injurious bacteria (row 5) are 

 the results of starvation (Table LIIL, and row 6, Table XVIII. ). 

 The starving culture consisted of individuals from the same culture 

 as row I, placed in fresh hay infusion June 14. The constants 

 before they were placed in the hay infusion are given in row i. Table 

 XVIII., while the immediate effects of the infusion are shown in 

 row 2 of the same table. The same animals were left in this fluid 

 for eleven days, till June 25. They had evidently begun to starve; 

 they were small and thin and almost half of them had died. The 

 dimensions are given in Table LIIL, and the constants in row 6, 

 Table XVIII. The length had fallen from 184.680 to 149.360 

 microns ; the breadth from 64.880 to 38.080 microns. The breadth 



