326 GRIFFIN. 



as its importance then was not appreciated. Plate V, figure lH, and Plate 

 VI, figure 24, are both drawings of sections passing througli the aperture 

 of the peristomial invagination. 



The further development of the peristome and pharynx proceeds as the 

 body divides. The body of the Euplotes elongates a little before any 

 constriction appears. This change in shape is made evident by the new 

 peristome moving backward, as if it were pulled out from beneath the old 

 one. (Plate YIII, figures 33 and 34.) By the time that the constric- 

 tion of the body can be noticed, the opening of the new peristome to the 

 exterior has become large, extending from the posterior margin of the old 

 peristome to the posterior end of the new one. (Plate VIII, figure 34.) 

 At the same time the anterior end of the peristomial invagination bends 

 toward the middle of the body. Plate VIII, figures 34, 35, and 36 are 

 successive drawings of one individual, made at intervals of about half 

 an hour; they illustrate the manner in which constriction of the body, 

 further increase in the size of the opening of the new peristome, and 

 bending of the anterior end of the new peristome toward the right, pro- 

 ceed simultaneously. In Euplotes harpa the curvature of the anterior end 

 of the new peristome toward the right commences at a very early stage, 

 even before the invagination has attained its full length, and long before 

 constriction of the body begins. There is also in that species an inward 

 bending near the middle of the new peristome which is altogether lacking 

 in E. wmcesteri. The anterior end of the adoral zone lies in a cavity 

 derived from the original invagination (Plate VII, figure 37, and Plate 

 VIII, figure 36) until fission is nearly comi^lete. As the constriction of 

 tlie body deepens, the adoral zone is more and more uncovered, reaching 

 the adult condition while the two bodies are still connected. (Plate VII, 

 figures 28 and 29.) 



While the anterior end of the peristome is passing across the end of the 

 body, the pharynx moves still more toward the center of the body and 

 its tip bends forward. (Plates VII and VIII, figures 26, 28, 34, 3.5, 36.) 

 The widening in which the suboral membranclke appear develops into 

 the anterior expansion of the pharynx, in which the rows of endoral cilia 

 appear before tlie constriction of the body is far advanced. (Plate VIT, 

 figure 26.) 



The medial margin of the peristome is not derived from the inner 

 edge of the growing aperture of the invagination, but from a ridge which 

 grows fon\'ard from the anterior angle of the mouth across the medial 

 wall of the peristomial depression. Plate VII, figure 26, Plate VIII, 

 figures 34, 35, and 36, show successive stages in the development of this 

 feature. As in Euplotes harpa, this ridge divides the right wall of the 

 peristomial cavity into two portions; the dorsal portion becomes the inner 

 wall of the completed peristome, while the ventral moiety becomes included 

 in the ventral surface of the body. The part of the ventral covering of 



