xv, 4 Be Leon: Balantidium Haughwouti 395 
conditions* the animal maintains a constant body form and 
externally is bilaterally symmetrical. When disturbed, however, 
as when it is placed in a foreign medium, the animal can assume 
a slipperlike form with marked flattening. This may at times 
give an appearance superficially resembling that of Paramoecium 
caudatum. This illustrates the marked plasticity of the or- 
ganism. When placed under restraint, as by pressing the cover 
glass down against the slide, or when the animals are compelled 
to swim through tangled strands of cotton, this plasticity enables 
them to assume shapes so varied that when seen for the first 
time under such conditions they might almost be mistaken for 
amoebse. This is a phenomenon of frequent occurrence among 
the Ciliata. 
Placed in their natural medium, that is to say, the intestinal 
juice of the host snail, these organisms can be seen to progress 
evenly and gracefully with a slight rotary motion. When slightly 
disturbed or placed in a foreign medium they move rapidly 
by a series of jerks and dashes and sudden turns, coupled with 
vigorous rotation about the long axis. When put under pressure 
or placed under some obstruction the animals take on the 
“amoeboid” movement before mentioned, the elasticity and the 
flexibility of the cell wall ]?eing well shown under these con- 
ditions. This movement, however, is not amoeboid movement 
in the true sense. 
Furthermore, the anterior end of the animal seems capable 
of protrusion to a considerable extent, and it is likewise capable 
of flexion in every direction. In this respect the anterior end 
of the animal really behaves very much as does the pseudopo- 
dium of a rhizopod, apparently serving to guide the animal in 
forward progression among obstacles. The rest of the body 
follows by successive regional contractions and adaptations of 
the cell wall accompanied by rapid cyclosis of the endoplasm in 
the direction of the anterior end. The coarsely granular pro- 
toplasm, the nuclei, and the vacuoles follow the anteriorly sit- 
uated finely granular endoplasm. 
This species is one of the smaller of those included in the 
genus Balantidium. Its average length, computed from a series 
of fifty individuals selected at random, was 50 the average 
width was 40 n. The animal is widest at the posterior third 
of the body, the anterior third being the narrowest portion. 
