Paramecium trichium typically ranges in length from 50 μ to 105 μ, with the majority falling between 80 μ and 90 μ. Its width varies between one-third and one-half of its length, with a somewhat flattened dorsoventral profile. A broad buccal groove extends diagonally from the anterior left border across the ventral surface to the mouth, usually situated slightly anterior to the midpoint and to the right of the median line. The mouth leads into a relatively elongated cytopharynx containing an undulating membrane. The cytopyge is positioned subterminally, while a small caudal tuft of longer cilia is subapical. The flexible outer layer, or ectosarc, contains numerous trichocysts. Contractile vacuoles are found near either end, deeply situated and exhibiting a more intense staining compared to the surrounding protoplasm. In vivo, there seem to be two contractile vacuoles, which contract alternately, with smaller ones adjacent. Contractions occur at a rate of fifteen to twenty-five per minute. The macronucleus is of medium size, and a single micronucleus is of the ‘caudatum’ type. Binary fission in Paramecium trichium appears to be triggered by a metaphase-like state of the micronucleus. This is followed by significant enlargement and eventual separation of the chromatin threads into two anaphase groups. Notably, the metaphase appears to precede the changes analogous to prophase seen in other instances. Throughout the body division process, the two existing contractile vacuoles persist.