Studies on the Life History of Protozoa. 461 



Fig. 13. Another individual treated with potassium phosphate. The micronucleus is separated 

 from the macronucleus. At the lower end the focus is sufBciently sharp to show the characteristic 

 papilli-form structure of the trichocyst spaces in the ectoplasm. 



Fig. 14. One of the last individuals of the B series (504th generation) in which the macronucleus 

 is entirely gone. The micronucleus is distinct, and has its chromatin massed near one pole. The place 

 which held the macronucleus is marked by a large vacuole. There are no observations to indicate the 

 fate of this macronucleus, the break at the left side indicates that it may have dropped out at some period, 

 although this did not happen during the course of the treatment, because the same condition was 

 observed during its life, and immediately after killing. 



Fig. 15. An individual from the B series in the 502d generation after treatment with beef extract. 

 The characteristic dense endoplasm is still present but there are many gastric vacuoles, while the micro- 

 nucleus has divided three or more times and the daughter nuclei have accumulated at one end. 



Fig. 16. An individual of the A series in the 6o2d generation treated for 25 minutes with phos- 

 phoric acid. It was transferred to hay infusion and killed 24 hours afterwards. The macronucleus is 

 broken into fragments; the micronucleus has divided and one part (left center) seems to be forming a 

 new macronucleus. (This individual offers the only evidence obtained of nuclear fragmentation and 

 reconstruction through artificial means.) 



Fig. 17. An individual from the A series in the 718th generation, killed October 20 after living six 

 days without division. The endoplasm shows a general absence of the larger granules, indicating 

 starvation; the micronucleus (dimly visible at the lower end of the macronucleus) is hyaline and without 

 chromatin, evidently degenerated. 



Fig. 18. Two individuals of the A series in the 6o2d generation, treated with a dilute solution of 

 sodium chloride (see description), for 25 minutes. Transferred to hay infusion 24 hours afterward, 

 and killed. 



Plate III. 



Figs. 19, 20, 21 and 22. Four individuals at the end period of the A series. Note that in all of 

 these the macronucleus is not abnormally large as compared with normal individuals. This was true 

 throughout the entire race at this period and contradicts Hertwig's recent theory of the size-relations at 

 periods of depression. Fig. 19 represents an individual in the 720th generation, unusually small and 

 unlike the remainder of the culture at this time. Fig. 20 represents an individual in the 725th 

 generation, with conspicuously dense endoplasm and macronucleus. The latter bulges out towards the 

 observer and the effect of the ectoplasm about it is that of a special nuclear capsule. Fig. 21, an 

 individual in the 741st generation showing the looser texture of the endoplasm, gastric vacuoles and other 

 characters, indicating that these organs had been restored by stimulation. The micronucleus is hyper- 

 trophied, the macronucleus is normal. Fig. 22 represents an individual in the 742d generation, the 

 oldest of the race. It shows the reorganized endoplasm, gastric vacuoles, and the like, but ectoplasm 

 and micronucleus are degenerated. The former by vacuolization (note punctate appearance on right 

 of macronucleus) the latter by hypertrophy and loss of chromatin. 



Figs. 23 and 24. These represent individuals which were starved for two and four weeks respect- 

 ively. Those in Fig. 23 were fed on beef extract August 19, transferred to hay August 20th and left 

 unchanged until September 19, when they were killed. The individual shown in Fig. 24 was not given 

 beef extract, but was left in hay infusion for two weeks unchanged, when it was killed. In Fig. 23 

 the spots at the lower ends represent the micronuclei, in Fig. 24 the upper elongated granule is the 

 micronucleus. 



Fig. 25. A triple monster from an individual 72 hours after conjugation, with many nuclear frag- 

 ments and evidence of two incomplete divisions. 



Fig. 26. A double monster from the A series in September, 1901. The micronucleus is undivided, 

 the macronucleus is deeply cleft and the individual on the right has no trace of nuclei. 



