April, 1905.] Epistylis flavicaim. 327 



THE RATE OF GROWTH IN EPISTYLIS FLAVICANS. 



F. L, Laxdacre. 



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 may 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. Dtiring 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 still 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-thircl of the total body length and extending proximally 

 from the posterior circlet of cilia. The body had begun to 

 assume the normal shape the adoral cilia were vibrating and the 



