344 Ufiiversity of California Puhlications in Zoology [Vol. 18 



STRUCTURE 



External Features 



Euplotes patella is, in general shape, oval with the anterior end 

 slightly truncated. In a study of many hundreds of individuals, it 

 has been seen that the sides are normally nearly parallel, but occasion- 

 ally a culture will develop for a few days in which animals are found 

 with wide lateral winglike outgrowths, so that at the widest part the 

 animal is almost as wide as long. No reason can be ascribed for this 

 phenomenon, since all of the cultures were kept under as nearly the 

 same conditions of food, temperature, concentration, etc., as possible. 

 The average length of E. patella is one hundred forty-five microns 

 while its width is about ninety microns. The average size of indi- 

 viduals will vary in different cultures from animals recently divided, 

 which are about two-thirds the average size, to animals fifteen to 

 twenty microns in excess of the average length. 



When viewed from the dorsal side, Euplotes patella appears almost 

 bilaterally symmetrical, but a ventral view shows that the arrangement 

 of the cirri and membranelles and position of the cytostome make the 

 animal very asymmetrical (pi. 14, fig. 4). 



The ventral side of E. patella is concave, rather strongly so anter- 

 iorly, but flattening out posteriorly. The dorsal side is strongly con- 

 vex in the middle part, but flattens out toward the edges where the 

 dorsal and ventral surfaces meet at an acute angle forming a sharp 

 edge. The dorsal surface is marked by eleven rows of rosettes of 

 granules (pi. 14, fig. 7). Griffin (1910) describes the rosette arrange- 

 ment of granules in E. worcesteri and claims that at the center of the 

 groups there are sensory bristles. Such sensory structures have never 

 been figured for Euplotes patella and I have been unable to see them 

 either on living or stained specimens. 



As described above the ventral side of Euplotes patella is char- 

 acterized by the presence of cirri and membranelles arranged in a 

 characteristic and constant manner (pi. 14. fig. 4). These styliform 

 cirri, the minute structure of which will be described later, fall into 

 four groups. The six frontal cirri are grouped roughly into two rows 

 of three each. These rows rtm from the right anterior corner of the 

 cytostome to the right edge of the animal. Slightly posterior to these 

 are three scattered ventral cirri. About two-thirds of the distance 

 from the anterior end are five large heavy anal cirri, which extend 



