250 University of California Publications in Zoology [ VoL - 20 



ior to its midpoint; the adoral zone is approximately terminal, and 

 the anterior tip of the body lies within it; the plane of demarcation 

 between the apical cone of the ectoplasm and the endoplasm is approx- 

 imately at right angles to the long axis of the body ; the macronucleus 

 is elongate but the length usually does not exceed three times the 

 breadth; two contractile vacuoles are present, a smaller one located 

 anteriorly and a larger one located posteriorly; a posterior cytopyge 

 is usually distinctly visible. 



BALANTIDIUM suis SP. NOV. 



Early in the work of examining pigs for Balantidium coli it became 

 evident that this protozoan showed extreme variation in shape. In 

 many instances the diversity occurred among individuals from the 

 same host. Further observations led me to believe that there were 

 two fairly distinct types, the one, longer and more slender as compared 

 with the other which was distinctly ovoid. Measurements have been 

 recorded by various writers of Balantidium coli from man. Malmsten 

 (1857) in the original description gave the length as 60-10CV; breadth, 

 50-70/i. Solojew (1901) recorded the length as 65/*, the breadth as 

 40/A. Wising (1871) states that the length varies from 50-100/z, while 

 the breadth varies from 40-50/*. Prowazek (1913) gave the length as 

 52-71/x, the breadth, 40-58/*. Leuckart (1861) measured balantidia 

 from swine and found the length to be 75-110/x and the breadth 70/x. 

 Still others give dimensions, but all are inadequate for the determina- 

 tion of the occurrence of types with distinct proportions. First, with 

 one or two exceptions all dimensions have been taken of balantidia 

 found in man, and from these it might not be safe to draw conclusions 

 regarding diversity among those found in pigs. In the second place, 

 the measurements given are either averages or else represent extreme 

 limits. In either case they are practically useless in determining indi- 

 vidual variations, for even in the case of extreme types the range 

 between limits is so great that two, or even more, distinct types, based 

 on proportions of breadth to length, might be included. Nowhere 

 has there been found a series of individual measurements which would 

 make it possible to determine whether variations were continuous or 

 discontinuous. To obtain such a series of measurements was the pur- 

 pose of the phase of the work about to be described. 



Material which was to be used in taking the measurements was 

 killed and preserved with all possible care. Hot Schaudinn's fluid 

 was used in all cases, the material being quickly and thoroughly mixed 



