2 2 6 JOHNSON. [Vol. V 1 1 1 . 



4. After enfeeblement or degeneration of organs of nutri- 

 tion. Complete atrophy of old pharynx, and partial atrophy of 

 old frontal field and zone. 



5. After conjugation (I) Not yet observed in Stentor. 

 Has been recorded in Spirostomum (Maupas, '89) and many 

 other Infusoria (Maupas, R. Hertwig, '89). 



On every occasion when regeneration is required, it is car- 

 ried out in the same manner. In no instance have I followed 

 the development of a new oral apparatus that did not entail 

 meganuclear reconstitution. There is a subtile bond of union 

 between the two phenomena, and the characteristic condensa- 

 tion of the meganucleus cannot be regarded as an intrinsic 

 part of the process of fission alone. It is of interest to note, 

 furthermore, that the meganucleus in no case takes the initia- 

 tive; the cytoplasmic change invariably precedes the karyo- 

 plasmic, thus reversing the order of events prevailing in cell- 

 division in Metazoan- and plant-cells. 



I have made repeated experiments to ascertain whether 

 membranellae could be regenerated in any except the 

 ordinary way. The adoral zones of Stentors were damaged 

 with the needle in various ways and at different points, 

 and portions of the zone were amputated with the scalpel. 

 If the injury was slight, the wound closed up, bringing the 

 cut ends of the zone into contact, so that the zone was, 

 apparently, as good as ever. If enough of the zone was cut 

 away to interfere seriously with its function, membranellae 

 were never formed in place of the lost ones; the loss was 

 made good by regeneration in the usual way. The result 

 of the experiments led me to the conclusion that the regenera- 

 tion of the oral structures of Stentor does not take place in 

 situ. As would be expected, injury to or removal of the adoral 

 portions of the zone, especially if affecting the pharynx, were 

 more likely to cause regeneration than injuries to the aboral 

 portions. 



Just as among pluricellular beings the regeneration of highly- 

 specialized organs always takes place from the least differen- 

 tiated cells available, so among unicellular organisms the more 

 specialized portions ("organula") of the cell are regenerated 



