46 Uiiiversifii of California Pitblicafions in Zoology [Vol. 20 



be protruded a short distance (fig. C, 1, 2, 8) or may be deeply with- 

 drawn (fig. C, 5). The membrane forming the caplike covering is 

 thin, remarkably transparent, and does not stain with any of the 

 reagents used in the preparations of the material. 



The body is radially symmetrical with graceful outlines. All 

 trace of the characteristic asymmetry of the flagellates is lost. Its 

 length is two or three times its greatest transdiameter which is in the 

 posterior third of the body. The shape of the body may vary consid- 

 erably from the campanulate form. The early prophases of division 

 are marked by a characteristic rounding up of the entire body (pi. 7, 

 fig. 31). The variation in shape in the ordinary trophozoite stage are 

 less marked. Some of these are shown in figure A. The anterior half 

 of the body is more stable in its outlines than is the posterior half 

 and shows fewer metabolic changes. It may become thickened, losing 

 the graceful curved lines, becoming conical in shape (fig. A, 4), or 

 with a transdiameter equal to that of the posterior part (fig. A, 1). 



It is in the posterior half of the body that the most striking varia- 

 tions are found. This is covered only with a thin periplast in contrast 

 with the thick ectoplasm of the anterior part (fig. B). As a result of 

 this condition it is the most delicate part and the one which most 

 frequently shows the effects of injury in the manipulation of the 

 material and its preparation for microscopical examination. In addi- 

 tion to this individuals are sometimes found which show metabolic 

 changes in the posterior part of the organism, which are not the 

 result of injury but may possibly be due to some chemical changes in 

 the surrounding medivun. These changes are shown in figures A, 2-4. 



The posterior part may be drawn out into a slender cylinder 

 with a consequent shortening of its transdiameter, and may some- 

 times equal or even exceed the length of the remainder of the body 

 (fig. A, 2). Individuals thus affected have been observed in living 

 material and appear normal in other respects. 



In size this is the largest known species in the genus Tricho- 

 nympha. In general length it varies from 250 to 460^ and in width 

 from 110 to 200/t. The average length is about 350/^. A frequency 

 curve plotted from 121 measurements had its mode at 360/* and a slight 

 right-hand skew. Trichoiiympha agilis, as figured by Leidy (1881) 

 and Porter (1897), varies in length from 60 to about lOOjix, and for 

 T. hertwigi Hartmann (1910) gives the length as between 260 and 

 330/i. The latter species equals in length many individuals of T. 

 campanula, but falls short of the larger specimens, as well as having 



