1922] McDonald: On Balantidium coli and Balantidium suis 259 



in figures D, E, F, G, and H. The one form resembles very closely 

 a hen's egg, the small end being anterior. In this case the longest 

 diameter crosses posterior to the midpoint of the longitudinal axis. 

 In the elongate type, usually the posterior end is as much drawn to 



Figs. D-H. Camera lucicla drawings of Balantidium suis sp. nov. (figs. D 

 and E), and Balantidium coli (figs. F, G, and H), showing specific differences. 



a point as is the anterior, and often more so. In these cases the longest 

 diameter intersects the longitudinal axis at or anterior to its midpoint. 

 Coincident with the taking of measurements a careful search was 

 made to detect other morphological differences which might occur 

 between the two forms and be of aid in distinguishing one from the 

 other. The earliest difference to be noted related to the macronucleus. 

 The macronucleus in the ovoid type is relatively short, being approxi- 

 mately !/3 the length of the entire organism. It is customarily bean- 

 shaped in appearance, but may be almost straight or so sharply bent 



