April, 1905.] 
Epistylis flavican^^. 
327 
THE RATE OF GROWTH IN EPISTYLIS FLAVICANS. 
F. L. Landacre. 
The writer recently had an opportunity to observe the rate 
of growth in one of our common stalked Protozoa, Epistylis 
flavicans Ehr., and the changes in form of the animalcule which 
accompany this growth. 
A good deal of interest attaches to the rate of growth of the 
pedicle in stalked forms on account of the fact that two species 
frequently otherwise similar may be differentiated by the length 
of pedicle. A form with branched pedicle, which in its adult 
condition mav be easily differentiated by the pedicle, is with dif- 
ficulty separated from other species if its pedicle is still simple 
as it is in the earlier stages of growth. Each form having a 
branched stalk passes through a stage in which its stalk is simple 
and it is then sometimes with difficulty separated from the forms 
with unbranched pedicles. 
The frequency with which these immature forms are met 
with depends of course upon the time required for a detached 
zooid to acquire a pedicle characteristic of the adult form. If 
this is done uqickly, for instance, in a few hours, comparatively 
few immature forms would be encountered. If the period of 
growth is longer, for instance, several days or a week, one ought 
to find immature forms rather frequently. During the three 
summers spent in work on Protozoa at Sandusky no case of 
growth except the present instance was observed that could be 
measured. This may be due to the fact that work was com- 
menced about the first of June each year which would be after 
the period of maximum growth among the Protozoa, this period 
coming earlier in the spring. 
In the present case the attachment of the free swimming 
form was not observed. But in mounting a slide for observation 
a large colony of Epistylis flavicans was found many of whose 
zooids were detached and swimming about. Within a short time 
one was found attached and its rate of growth observed. It 
could have been attached only a short time for it st;ll had the 
typical cylindrical shape characteristic of free swimming forms 
(Fig. 1). The posterior circle of cilia. was vibrating rapidly and 
there was only a faint movement of the cilia visible in the region 
of the gullet. 
In three minutes it had assumed the form of Fig. 2. The 
posterior cilia were vibrating a little less rapidly. There was a 
cone shaped extension at the posterior end of the body equalling 
one-third of the total body length and extending proximall}^ 
from the posterior circlet of cilia. The body had begun to 
assume the normal shape the adoral cilia were vibrating and the 
