No. 3-] MORPHOLOGY OF THE STENTORS. 525 



The table shows that there is by no means always an 

 increase of nodes; sometimes there is even a decrease. In 

 regard to No. 13, there seems to be a reason for the great 

 reduction in their number. The Stentor was very small, and 

 the long nucleus, with its 19 nodes, almost filled the body. 

 The frontal field and adoral zone were almost atrophied, and 

 this circumstance was, unquestionably, the prime motive for 

 regeneration. I believe that in this case it was an advantage 

 to reduce the extent of the nuclear surface, and this was cer- 

 tainly accomplished by reducing the number of nodes. 



Although I have sectioned many specimens in various stages 

 of regeneration, I have not been so fortunate as to discover 

 the behavior of the micronuclei. The same difficulty encoun- 

 tered in the study of them at time of fission was met with 

 here — they become so transparent as almost always to escape 

 observation. The question. Do they divide at time of regener- 

 ation .'' therefore remains unanswered. If such should prove 

 to be the case, the extraordinary number of micronuclei in 

 Stentor would be accounted for. 



Doubtless the regeneration of buccal organs during the ordi- 

 nary condition of life obtains in all species of Stentor, and 

 may yet prove to be of wide prevalence among Infusoria. 

 Single stages were seen by Stein ('67) in 5. cceruleus, S. poly- 

 morplms and S. niger. Besides the Blue Stentor, I have 

 studied it in S.polyviorpJms, where it is carried out in the same 

 manner, and requires about the same length of time. 



3. Generalia. 



There are four — possibly five — occasions in the life-history 

 of Stentor when a regeneration of the oral organs is impera- 

 tive. They are: 



1 . Fission. New frontal field, adoral zone and pharynx formed 

 in toto for proximal individual. No atrophy of existing organs. 



2. After encystment. Not yet actually observed in Stentor, 

 but undoubtedly occurs. 



3. After amputation of, or serious mechanical injury to, 

 the organs of nutrition. Often atrophy of defective parts, 

 which are replaced by the newly-formed ones. 



