No. 3-] MORPHOLOGY OF THE STENTORS. 52 1 



the right side of the zone, and a narrow band it remains 

 throughout. It is a case of a rudimentary organ persisting 

 after its function has been assumed by another structure. 



The evolution of the zone and frontal field does not end with 

 Stentor, although in this genus these structures are completely 

 terminal. In Folliculina the field is produced into two lateral, 

 ear-like appendages. (Fig. Ill, /.) Unfortunately, we lack 

 sufificient information regarding the evolution of the new zone 

 in Folliculina to determine whether it has a Stentor-like stage 

 or not ; but the brief account of the fission by Mobius ('86) 

 shows that it is very aberrant, and obviously adjusted to the 

 peculiar mode of life and highly-modified frontal field of this 

 form. It is therefore improbable that it will reveal much in 

 regard to the phylogeny of Folliculina. 



C. Regeneration. 



One of the most remarkable events in the life-history of 

 Stentor is the periodic renewal of the mouth, pharynx, and 

 adjacent parts of frontal field and adoral zone. That Infusoria 

 are able to regenerate missing organs after encystment, con- 

 jugation, or merotomy, is well known. The peculiarity as 

 regards Stentor is that regeneration also occurs when the 

 parts to be renewed are already present and functional 



Considering the frequency of the regenerative process in 

 vS. ccsrulens, it is surprising that it so long escaped detection. 

 Specimens in course of regeneration were indeed seen by Stein 

 ('67) and Schuberg ('90). It remained, however, for Balbiani 

 ('91^) to discover the real character of the process, and follow 

 it through its stages. My own study of 5. ccBruleus had 

 included the regenerative phenomena, and I had seen every 

 stage of it previous to the publication of Balbiani's paper. 

 I am able, therefore, to confirm his results from wholly inde- 

 pendent observation, and add besides a few new facts. At the 

 outset, I regarded the process as an abortive fission, believing 

 that under certain circumstances the animal was unable to 

 bring division to a successful issue, and its new frontal field 

 then coalesced with the old, thereby inducing the atrophy of 

 duplicated parts. But observation of the fact that successful 



