6lO Lor and e Loss Woodruff. 



fused condition of the macronuclei similar to that in Fig. 2, though 

 the chromatic material appears somewhat more homogenous. 

 Here again the micronuclei, with two exceptions, are out of focus. 

 Other characteristic specimens of this period of declining vitality 

 are shown in Figures 5, 6, 7 and 8, all representing forms from the 

 243d to the 247th generation (cf. Explanation of Plates). 



The specimen illustrated in Fig, 9 is of the 250th generation 

 and is the last of the descending cycle of A-i, since on July 7, 

 1902, this line sprang into renewed dividing activity (cf. p. 592). 

 The marked improvement of the cytoplasmic and nuclear con- 

 dition of the infusorians is shown in an individual of the 256th 

 generation (Fig. 12). Here the macronuclei, in outline and in 

 general appearance, are again approaching the typical condition, 

 and the position of the micronuclei in relation to the macronuclei 

 is also more typical. Lines A-2, A-3, and A-4, however, which 

 remained dividing at the slow rate, show no improvement in their 

 nuclear condition, as is seen in specimens of the 255th generation 

 (Figs. 10 and 11). 



. The cytoplasm of the "rejuvenated" individual, from line A-i, 

 represented in Fig. 13 is still somewhat vacuolized, but the 

 macronuclei and micronuclei are nearly typical. The specimen 

 is quite small but this is due to the high rate of division prevailing 

 at this period. This reduction in size is still more apparent in 

 preparations of the 331st generation (Fig. 14), but beginning at 

 about the 409th generation (Fig. 15) the size again increases with 

 the slightly decreased fission-rate. This beautifully diagram- 

 matic condition of the nuclear apparatus is the prevailing state 

 in the large majority of specimens at this period of great repro- 

 ductive activity. One most interesting exception, however, is 

 that in tw^o lines of the culture, specimens from the 361st to 369th 

 generations lack the posterior micronuclear body. This is but 

 temporary and for almost one-hundred generations after this the 

 normal condition prevails. Preparations of the 458th generation 

 again show evidence of a changed condition of the micronuclei 

 since now they appear pale; the chromatin having but little 

 affinity for the stain. This peculiarity reaches a climax at the 

 473d generation when the micronuclei appear almost perfectly 

 clear; but from this time on they again resume their normaj 

 staining capacity. 



Starting at about the 542d^generation the cytoplasm shows signs 



