210 



THE AMERICAN NATURALIST [Vol. LI 



Trichomonas is found living in the intestinal contents 

 of nearly all animals and has, since its discovery by Donne 

 in 1837, appeared under many different names. It is a small 

 organism, built on an oval or pear-shaped plan, and meas- 

 uring in the adult trophozoite stage, about 10 fi in lengith 

 by 5 to 6;tt in breadth. The youngest free-swimming 

 stages are much smaller, about 5/* in length; and some- 

 times trophozoites are encountered that measure 12 or 

 ISfi. Although usually of an elongate oval or pear shape, 

 the morphology of the trophozoites is highly variable, and 

 triangular or crescentic forms are frequently encountered, 

 especially among the young. The anterior end is usually 

 blunt, while the posterior end is frequently drawn out into 

 a point. 



If one adds to the salt solution in which these flagellates 

 are being examined a little albumen or glycerin, to lessen 

 the rapid swimming of the organism, some of the details 

 of structure can be made out. The body plasm shows a 

 greenish tint, and the nucleus, which is situated an- 

 teriorly, appears pinkish. In fresh preparations, one of 

 the most obvious features is the axostyle, a short bristle- 

 like structure which projects outward somewhere in the 

 posterior quarter of the body, and which is seen, upon 

 careful focusing, to extend into the body of the flagellate, 

 running anteriorly to terminate somewhere in the vicinity 

 of the nucleus (Figs. 1, 2). Inside the body the axostyle 

 appears homogeneous in structure and bandlike. 



Next to the axostyle, the most obvious feature is the 

 vibratory or undulatory membrane which extends like a 

 curved fin down the dorsal side of the flagellate body 

 (Fig. 1). It is shallow at the beginning and at the end, 

 but midway of its length it may have a depth of 2 to 3 m. 

 Over this membrane may be seen to travel at 3 to 4/* in- 

 tervals, waves of motion from the anterior toward the 

 posterior end of the body. If one follows closely the. 

 course of this membrane, it is found to have its origin in 

 a granule, or in a group of small grnTiules, located in front 

 of the nucleus at the most anterior part of the animal, 

 and known as the blepharoplast-complex. The granules 



