The Life-History of Hypotrichous Infusoria. 631 



EXPLANATION OF PLATES. 



The photographs were taken by Dr. Edward Learning, of Columbia University, from permanent 

 preparations stained with picrocarmin. The magnification is the same in every case and the relative 

 sizes, therefore, represent absolute differences. The figures, unless otherwise specified, are of Oxytricha 

 fallax. Culture A. 



Plate I. 



Figs. I and 2. Two individuals in the 230th generation, period 16, April 2,1902. (C/. Diagram I.) 

 The cytoplasm is vacuolated and the macronuclei are vacuolated and displaced in the cell. A charac- 

 teristic "halo'' is visible about the macronuclei. The individual shown in Fig. 2 has three micronuclei. 



Figs. 3 and 4. Individuals in the 239th and 241st generation respectively. Period 24, June 1902. 

 The two macronuclei in each are fused and their structure appears somewhat more homogenous than 

 is the case in those illustrated in Figs. I and 2. 



Fig. 5. Specimen in the 243d generation, period 25, June 24, 1902, showing an extreme case of 

 cytoplasmic vacuolization. The nuclei are exceptionally normal for this period of the cycle. 



Fig. 6. Specimen in the 246th generation, period 25, July i, 1902. 



Fig. 7. Individual in the 246th generation (A-2), period 25, July 2, 1902. The macronuclei are 

 surrounded by a "halo'' (c/. Fig. i). 



Fig. 8. Individual in the 247th generation (A-i), period 25, July 2, 1902. Note the condition of 

 the cytoplasm. 



Plate II. 



Fig. 9. Specimen in the 250th generation (A-i), period 26, July 6, 1902. The cell is shrunken and 

 the cytoplasm considerably vacuolated. Note the somewhat reduced size and irregular contour of the 

 cell. This is the last of the line A-i before it was "rejuvenated." 



Figs. 10 and 11. Specimens in the 255th generation, period 27, July 21, 1902. These individuals 

 are from line A-2 which remained dividing, at this time, at the slow rate. The specimen photographed 

 in Fig. 10 has ingested a Trachelomonas volvocina. 



Fig. 12. Specimen in the 256th generation (A-i), period 26, July 8, 1902. This line had divided 

 six times within the past forty-eight hours. Note the normal condition of cytoplasm and nuclei as 

 compared with the preceding specimens. 



Fig. 13. Specimen in the 287th generation (A-i), period 27, July 20, 1902. Size is reduced. 

 Compare with Fig. 12. 



Fig. 14. Individual in the 331st generation (A-i), period 29, August 7, 1902. Size is reduced. 

 Nuclei are proportionately large. 



Fig. 15. Specimen in the 409th generation, period 32, September I, 1902. Apparently a "normal" 

 individual in every respect. 



Fig. i6. Specimen in the 542d generation, period 36, October 17, 1902. Cytoplasmic vacuoliza- 

 tion begins to appear. 



Fig. 17. Individual in the 829th generation, period 56, April 29, 1903. Nuclear fragmentation 

 has begun. 



Fig. 18. Specimen in the 853d generation, period 62, July 2, 1903. Nuclear and cytoplasmic 

 degeneration is far advanced. The size of the cell is greatly increased. 



