-o6 JOHNSON. [Vol. VIII. 



the cytoplasm. The new velum and buccal pouch (Figs. 33, 

 36, vel.^) become evident during the late stages of fission. The 

 formation of the new pharynx produces no break in the 

 integument, except at the inmost point where the mouth is 

 located, and the pharynx is, therefore, lined with an integu- 

 ment that once covered the surface of the body; it is compara- 

 ble to the stomodaeum of a Vertebrate embryo. 



As soon as the new pharynx begins to develop, the body of 

 the Stentor becomes considerably elongated and more cylin- 

 drical than in the usual condition. A slight constriction 

 appears about midway of its length (Fig. 27). This constric- 

 tion is probably a mere result of the elongation, and has 

 nothing to do with the fissional constriction which appears 

 later. It seldom or never coincides with the fission-line (Fig. 

 31). Synchronous with the constriction above-mentioned, and 

 perhaps a result of it, I have noticed a decided bend to the left 

 in the new adoral zone (Fig. 30). This bend is important as 

 indicating the point at which the fission-line starts (Fig. 31, /). 

 The formation of this cleavage line was first observed by 

 Moxon ('69), and has been accurately described by Schuberg 

 (p. 228). I have little to add to his account. Its advent is so 

 sudden, and it extends so rapidly around the animal, that it is 

 difficult to ascertain where it first appears. Schuberg states 

 that it starts on the left border of the new zone at the point 

 where the latter reaches the left boundary-stripe of the ramify- 

 ing zone. I am at least satisfied that this is the first point 

 where the fission-line touches the zone. Thence it passes to 

 the right around the body, cutting all the stripes at right 

 angles (Fig. 31,/) until it reaches the right side, where it 

 extends obliquely upward to meet the curved aboral end of the 

 new zone. I do not find that it approaches the new mouth so 

 closely as Schuberg has represented, but rather takes the direc- 

 tion shown in Fig. 33. At a slightly later stage the starting- 

 point of the fission-line is found to have passed above the 

 anterior curve of the new zone, now very pronounced, and to 

 have joined the other extremity (Fig. 22, /). The process by 

 which the transposition is brought about I have not been able 

 to follow. The constriction which at length separates the two 



