114 SECTIONAL ADDRESSES. 
under other conditions when conjugation was found to occur. Later 
observations by Erdmann and Woodruff show that a reorganisation of 
the nuclear apparatus of Paramecium takes place about every twenty- 
five to thirty days (forty to fifty generations). This process, termed 
endomixis (in contrast to amphimixis), seems to be a normal event in 
the several races of Paramecium which Erdmann and Woodruff have 
examined, and it is proved to coincide with the low points or depressions 
in the rhythm exhibited by Paramecium. The occurrence of endomixis 
raises the question, to which at present there is no answer, as to whether 
this process is necessary for the continued health of the nuclear 
apparatus and of the cytoplasm of Paramecium. 
Enriques (1916) maintained a ciliate—Glauwcoma pyriformis— 
through 2,701 generations without conjugation, and almost certainly 
without endomixis. From a single ‘ wild’ specimen he raised a large 
number and found that conjugating pairs were abundant, so that the 
objection could not be made that this was a non-conjugating race. 
Enriques then began his culture with one individual, and examined the 
descendants morning and evening, removing each time a specimen for 
the succeeding culture. The number of divisions per day varied from 
nine to thirteen, and as there was no break in the regularity and rapidity 
of division, and no sort of depression, Enriques concluded that neither 
endomixis nor conjugation could have occurred, for these processes take 
some time and would have considerably reduced the rate of division. 
These results, especially if they are confirmed by cytological study of 
preserved examples, show that for Glaucoma neither conjugation nor 
endomixis is necessary for continued healthy existence. Hartmann’s 
observations (1917) on the flagellate Hudorina elegans extend the con- 
clusion to another class of Protozoa. He followed this flagellate through 
550 generations in two and a-half years. The mode of reproduction 
was purely asexual, and there was no depression and no nuclear re- 
organisation other than that following fission. The evidence seems 
sufficient to confirm the view that certain Protozoa, if kept under favour- 
able conditions, can maintain their vigour and divide indefinitely, without 
either amphimixis or endomixis. 
Child (1915) states as the result of his experiments that the rate of 
metabolism is highest in Paramecium and other ciliates immediately 
after fission—‘ in other words, after fission the animals are physiolo- 
gically younger than before fission.’ This view, that rejuvenescence 
occurs with each fission, derives support from the observations of 
Enriques and Hartmann, for no other process was found to be taking 
place and vet the vigour of their organisms in culture was unimpaired. 
Tf, then, fission is sufficiently frequent—that is, if the conditions for 
growth remain favourable—the protoplasm maintains its vigour. Tf 
through changes in the external conditions the division rate falls, the 
rejuvenescence at each fission may not be sufficient to balance the 
deterioration taking place between the less frequent divisions. Under 
such conditions endomixis or conjugation may occur with beneficial 
results in some cases, but if these processes are precluded there is 
annarently nothine to arrest the progressive decline or ‘ ageing ’ ohserved 
hv Manpas and others. But further investigations are reanired on the 
physiology and morphology of decline in the protozoan individual. 
