EUPLOTES WORCESTERI: I. 293 



of the form of the bod}' aceomiJanied by changes in the shape and. fiosition 

 of the peristome frequently occurs. These abnonnal fonns probably are 

 the result of the same conditions which presently cause the death of the 

 greater part of the animals in the culture, that is, the accumulation of 

 waste products and toxins of the Euplotes themselves and of the bacteria 

 present. 



From Plate I, figure 1, and Plate II, figures 2 and 4, it will be seen 

 that the greater part of the peristome lies upon the ventral surface, in 

 the shape of a shallow depression the median wall of which is vertical, 

 while the lateral wall curves from the bottom of the peristome to the 

 level of the ventral surface. The anterior portion of the peristome passes 

 as a shallow^ vertical depression across the anterior end of the body to the 

 right side. The innei- wall of the peristome turns abruptly to form the 

 ventral edge of this groove, while the lateral edge of the peristome passes 

 over the left edge and then across the anterior end of the body. The 

 anterior portion of the peristome is slightly overhung by the projecting 

 dorsal surface. 



A thin lamella projects from the margin of the inner wall, com- 

 mencing at the right end of the peristome and continuing around the 

 angle of the median wall. The vertical anterior portion of the peristome 

 thus lies between the projecting ledge of the dorsal surface and the 

 marginal lamella. (Plate I, figure 1; Plate II, figure 2.) I have never 

 found this marginal lamella extending far back of the angle of the 

 peristome. Minkiewicz publishes several sketches showing it to extend as 

 far as the mouth in E. vannus. In other species of Euplotes, for example 

 E. Itarpa, the marginal lamella is developed to a much greater extent. 

 It is not vibratile, its function being purely passive. 



Posteriorljr, the lateral edge of the peristome turns toward the mid-line 

 in a graceful curve, which is continued into the posterior w^all of the 

 Ijharynx. The posterior margin of the peristome is deepest next to the 

 mouth, and the lateral wall becomes more and more nearly vertical as 

 it approaches the mouth. The inner margin of the peristome sometimes 

 stops where it joins the outer margin back of the mouth, bitt usually 

 continues as a low ridge for a little distance past that point. A slight 

 citrvature of the inner wall of the peristome occurs below the mouth. 

 (Plate I, figure 1, Plate II, figure 4.) The adoral zone of membranell^ 

 lies close against the outer margin of the peristome, leaving the median 

 portion of the groove free from cilia or other vibratile organs. 



The ventral surface curves dorsad rather abruptly back of the five large 

 anal cirri, then again becomes horizontal; the caudal end of the body is 

 thus much thinner than other parts. A low ridge extends along the right 

 margin of the ventral surface. Each of the anal cirri stands in the 

 posterior end of an elongated depression of the surface, separated by ridges 

 which attain a far greater development in other species of the genus. 



