xv >* De 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 Para?noecium 

 cavdatum. 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 

 amoeba?. 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. WTien put under pressure 

 or placed under some obstruction the animals take on the 

 "amceboid" movement before mentioned, the elasticity and the 

 flexibility of the cell wall being well shown under these con- 

 ditions. This movement, however, is not amceboid 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 

 t|je 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 p; the average 

 width was 40 /a. The animal is widest at the posterior third 

 of the body, the anterior third being the narrowest portion. 



