PLATE 1 



EXPLANATION OF FIGURES 



These photographs were taken from permanent preparations stained with pic - 

 rocarmin. The same magnification was used in all cases and, therefore, the rela- 

 tive sizes represent absolute differences in the size of the different individuals. 



1 A typical, normal individual from the beef cultures. This specimen was tak- 

 en from the Sbhb culture at the 480th generation just prior to the June epidemic 

 of conjugation. 



2 to 6 These figures show non-conjugating animals in different stages of degen- 

 eration. They were preserved at different times during the February epidemic in 

 the Sb culture. The cytoplasmic structure shows great irregularities. The micro- 

 nuclei are to be seen in all the individuals but they are considerably enlarged and 

 shifted from their normal condition. The macronuclei have lost their character- 

 istic shapes. Figure 6 shows a very advanced stage of degeneration. 



7 to 8 Two individuals from the Sbh culture kept on the hay infusion medium. 

 Figure 7 was preserved at the time of the February epidemic in the Sb culture and 

 was at the 321st generation. Figure 8 is an individual preserved shortly before 

 the death of the Sbh culture at the 510th generation. No degeneration can be 

 noted.' One of the micronuclei can be seen in mitosis. The other micronucleus 

 is in the same stage but is out of focus. 



9 A pair of conjugants preserved during the June epidemic. This represents 

 an earl}' stage in conjugation before great change has taken place in the nuclear 

 structure. 



10 This pair of conj ugants was preserved during the February epidemic and shows 

 a somewhat later stage than figure 9. In the animal to the left can be seen thatwo 

 micronuclei in the spindle stage of mitosis just previous to the first maturation 

 division. The same stage is present in the other animal but is out of focus. 



11 A pair' of conjugants preserved during the February epidemic. In the 

 animal to the right can be seen what is interpreted as a copulation nucleus. The 

 same stage is out of focus in the other animal. 



12 A pair of conjugants preserved during the February epidemic. This is a 

 stage just previous to the separation of the gametes. 



13 tol5 Three typical specimens of ex-conj ugants preserved during the Febru- 

 ary epidemic. Figure 13 is a stage shortly after separation. Figure 14 shows a 

 stage in which degeneration has begun and in figure 15 an individual well advanced 

 in degeneration is shown. 



