No. 3-] MORPHOLOGY OF THE STENTORS. 50I 



external or cytoplasmic phenomena have been studied more 

 frequently and are more accurately known than the nuclear 

 changes, our knowledge of the latter being wholly due to the 

 researches of Stein and Balbiani, made long before the discovery 

 of modern cytological methods. 



It was not until I had made considerable progress in the 

 study of the fission of .S. ccericleiis, that I had access to 

 Schuberg's account of it. I continued the work in order to 

 test his results by personal observation, and perchance add 

 something to his important contribution to the subject. I 

 have, furthermore, thought it desirable to publish a series of 

 drawings (PI. XXIV, Figs. 26-37) illustrating the stages of 

 fission of wS". cceruleiis ; for hitherto no complete and accurate 

 series has been given for any species of Stentor. These figures 

 obviously do not represent successive stages in the bipartition 

 of one individual ; for that, by reason of the occasional change 

 of position and contraction of the animal, I have found im- 

 practicable. 



I. Cytoplasmic PJiases. 



The first sign of fission is the formation of a rift (the anlage 

 of the new adoral zone) in the pellicula and ectoplasm near to 

 and almost parallel with the left boundary-stripe of the rami- 

 fying zone. (Fig. 26, a.z.^) This cleft has an early longitudinal 

 direction; yet, as Schuberg has already shown, it cuts across the 

 stripes of the ramifying zone, forming narrow angles with them 

 (Fig. 26). Schuberg represents the anlage of the new zone as 

 being very short at the outset, and gradually extending at the 

 extremities, which curve more and more toward the right. 

 This very early stage appears to be extremely transient, for out 

 of the many specimens I have studied in the first stages of 

 fission, I have seen but one or two that had a short rift. 



The rift opens at the outset to the full width of the adoral 

 zone. It opens entirely through the ectoplasm, as shown by 

 the absence of pigment, so that the soft endoplasm is exposed 

 and protrudes a little. From the start it exhibits a ciliary 

 motion. At the very beginning this movement seems as 

 undefined as that of the protruding cytoplasm of the foot; 



