The Ltje-History of Hypotrichous Infusoria. 6ll 



of vacuolization, and this increases steadily and at approximately 

 the 6ooth generation the nuclear apparatus begins to differ from 

 the normal. An early stage is shown in Fig. i6, and a later 

 stage exhibiting nuclear fragmentation in Fig. 17. The last 

 stage in this cytoplasmic and nuclear degeneration is shown 

 by specimens of the 853d and 854th generations (Figs. 18, 19 

 and 20) in which the cytoplasm is greatly vacuolated, the ventral 

 cirri reduced, the macronuclei distorted and fragmented, and the 

 micronuclei increased beyond the typical number; a condition 

 closely similar to that which obtained at the 230th generation 

 (Figs. I and 2). The series died out at the 860th generation 

 (c/. p.594). 



An interesting feature is the marked variation in size of the 

 infusorians at different periods of the life-cycle. Previous 

 workers have found that a gradual decrease in size occurred as 

 "old age" ensued. This certainly does not hold for the species 

 in question. Fig. 15 shows about the typical relative size of a 

 normal specimen, and a comparison of this with the figures of 

 the succeeding generations and with Figs, i through 8 shows 

 that the size gradually increased as the rate of division decreased. 

 This, however, is true only up to a certain point for, during 

 the last two days before death, the size decreased quite rapidly, 

 a decrease due to a shrinking of the cytoplasm which pro- 

 duced a more or less abnormal contour of the individuals. 

 This condition is shown somewhat inadequately in the speci- 

 men illustrated in Fig. 9, which is the last of the line before 

 the culture was " rejuvenated " in July, 1902. After this recupera- 

 tion, however, the size of the infusorians decreased remarkably 

 (from the normal) with the high rate of division {cf. Figs. 13 and 



The B-culture of Oxytricha {cf. Diagram II), which was 

 lost by accident at the 429th generation, shows far less fluctua- 

 tion in vitality than does culture A, indicating that the potential 

 of vitality of the B-series was considerably greater. Cytological 

 study of the preparations made from time to time shows that, 

 beginning at about the 140th generation and extending over 

 approximately the ensuing seventy-five generations, the anterior 

 micronucleus was not present. This was the only morphological 

 change apparent during the life of this culture. A typical speci- 

 men in the 365th generation is shown in Fig. 22. 



