No. 3-] MORPHOLOGY OF THE STENTORS. 51 I 



twin Stentors at once, but more often they remain connected 

 for some time by a thin cytoplasmic thread from the truncated 

 tip of the anterior Stentor. (Fig. 37.) The point of attach- 

 ment to the proximal zooid is always at the aboral extremity 

 {d.as}) of the adoral zone. The body stripes of the posterior 

 zooid are strongly curved towards this point, and this character, 

 combined with the notable roundness of the body-portion of 

 this zooid, as compared with the distal one (Fig. 36) serves to 

 distinguish the daughter-stentors for an hour or two after 

 fission is completed. 



The time consumed by fission in Stentor doubtless varies in 

 the different species, although I have found it approximately 

 the same in 5. ccBriileiis and .S. polymorpJms. It has been 

 variously stated. Stein ('67) was unable to give its duration, 

 but was correct in saying that the early stages require more 

 time than the later. Cox ('76) stated the period as only two 

 hours for S. polymorphiis — an understatement due to the fact 

 that he did not see the slow early development of the new 

 zone. Schuberg ('90, p. 225) estimated it at six and one-half 

 hours for 6". c<zr7ileiis, four hours being consumed in the early 

 formative stages, and two and one-half in the actual fission. I 

 have found that the duration of the process in 6". ccenileiis varies 

 somewhat according to the vigor of the animal, and doubtless 

 also according to the temperature, but my observation of it 

 at i7°-20° C. agrees very closely with Schuberg's. I have 

 repeatedly observed a period of about seven hours, but it is 

 sometimes an hour or more less. 



It is seen from the foregoing description that the cytoplasmic 

 phases of bipartition are divisible into two periods, the forma- 

 tive period, in which the anlagen of new organula are laid down, 

 and the constnctional period, during which the actual fission 

 takes place. As we shall see later in the consideration of 

 Regeneration in Stentor, it is in all probability the constriction 

 and not the neoformation of organula, that determines whether 

 fission shall take place, or merely renewal of mouth and adoral 

 zone. Our ignorance of the primiim movens to a neoformation 

 is complete. We can only say it lies in some peculiar molecular 

 condition that incites the duplication of existing organs. And 



