PARAMOECIUM POSSESSING EXTRA VACUOLES 291 



saturated with mercuric chloride). Animals fixed in this way 

 can be immediately cleared in glycerine which brings out many 

 of the internal parts very well, and the vacuoles, if they happen 

 to be expanded at the time of fixation, are visible. For whole 

 mounts and sectioning, paramoecia were fixed in Schaudinn's, 

 Gilson's, Flemming's and Worcester's solutions. As com- 

 paratively little time has been devoted to cytological studies I 

 am not prepared at present to offer any criticism of the fixatives. 

 To Dr. M. H. Jacobs I am indebted for his constant interest, 

 advice and criticism during the progress of the work recorded 

 here and I also feel under great obligation to the other mem- 

 bers of the Zoological Department of the University of Penn- 

 sylvania whose many kind suggestions have been of great 

 assistance to me. 



III. MORPHOLOGY 

 a. General description 



In general form, the animals of this race are apparently 

 identical with the common slipper-shaped Paramoecium cauda- 

 tum. The newly discovered individuals average rather larger 

 than any of the representatives of the two-vacuoled race I have 

 found about Philadelphia. Chart 1 shows a curve plotted to 

 illustrate the range in size. The peak of the curve is at 233 n 

 and is very nearly midway between the two extremes. On this 

 same chart are plotted the ends of two curves formed by animals 

 taken about Philadelphia. The range of one race is from 153 /x 

 to 207 M and in the other from 106 /x to 173 //• In the collection 

 of slides belonging to the Department I have found paramoecia 

 somewhat larger than the new race ranging from 197 ^ to 325 n. 

 The extremes of all the races studied by Jennings were 50 ^ and 

 332 M. 



In certain cultures where the individuals were unusually fav- 

 orable for study a band slightly darker than the surrounding 

 protoplasm could be seen across the center of the animal in the 

 region where the constriction appears at the time of division 

 (figs. 4 and 6). It is interesting to note that in these cultures 



