230 LORANDE LOSS WOODRUFF 
each of these lines practically every day up to the present time, thus 
precluding the possibility of conjugation taking place between 
sister cells. The number of divisions of each line has been recorded 
daily at the time of isolation and the average rate of these four 
lines has been again averaged for ten-day periods (cf. fig. 1). 
The culture medium has consisted of materials collected prac- 
tically at random from laboratory aquaria, hay infusions, ponds, 
etc. The infusions were thoroughly boiled to prevent the con- 
tamination of the pure lines of the pedigree cultures by ‘wild’ 
individuals. Permanent preparations have been preserved from 
time to time for the study of the cytological changes during the 
life history. 
In the light of this experience with cultures I shall consider 
each of the characters emphasized by Maupas. 
Shape. The general shape of the aurelia and caudatum forms 
is, in nearly all specimens, quite distinctive; aurelia is slightly 
more broad at the posteriorthan at the anterior end, while cau- 
datum, as the name implies, is quite pointed at the posterior 
end as compared: with the anterior end. The posterior end, in 
the specimens in my pure culture, is markedly pointed, and 
being free from endoplasmic inclusions, appears transparent and 
clearly delineated even under a lens with a magnification of ten 
diameters. ‘I have been accustomed to allow stock material 
from my pedigree aurelia culture to multiply in large flasks of 
hay infusion, for various experiments on conjugation, ete. 
Frequently I have used this material for my elementary class in 
biology and I have found that even the novice has called attention 
to the fact that the shape of the ends was reversed as compared 
with the figure of caudatum in the text-book. McClendon, how- 
ever, stated that in his study of aurelia and caudatum he found 
‘no characters of outward form” which were diagnostic. 
Changes in the vitality of my pedigree lines never have been 
very marked, and consequently I have not had organisms, in 
the direct lines of my pedigree cultures, representing physiolog- 
ical extremes to compare. Numerous experiments, however, 
have been made with ‘stock’ material left over after the daily 
isolations of the pure lines, which have clearly shown that, for 
