474 LORANDE LOSS WOODRUFF AND RH. ERDMANN 



Therefore the data justify the conclusion that this reorganiza- 

 tion process is a normal phenomenon and probably occurs in all 

 races of the species Paramaecium aurelia. 



Most suggestive observations on nuclear changes in Para- 

 maecium aurelia were made incidentally by Hertwig during his 

 study of conjugation in this species. This author noted ('89, 

 pp. 74-75) in a mass culture, in which conjugation had not been 

 observed for a long period, certain animals whose nuclear struc- 

 ture apparently indicates isolated steps in the phenomenon which 

 are described in detail in the present paper, and the significance 

 of which is here elucidated. 



Hertwig grouped the stages which he observed under two gen- 

 eral classes, one of which he interpreted as merely a vegetative 

 phenomenon, in which a new nuclear apparatus is not formed : 



Die zuerst eintretenden Veranderungen besitzen kein Analogon in 

 den Vorgangen einer normalen Entwicklung. Wahrscheinlich zerfallt 

 der Hauptkern erst in grossere dann in kleinere Stiicke, ohne das regel- 

 massige Auswachsen in Fortsatze, welches im Lauf der geschlechtlichen 

 Entwickelung der Paramaecium eintritt. Ich fand bald 2, bald 4 

 Nebenkerne entweder in Form der ruhenden Kerne oder haufiger in 

 Form von Spindeln, wie ich sie ebenfalls sonst nicht beobachtet habe. 



Our data show this to be a mistake. These stages are clearly 

 some steps in the descending phase of the process just before 

 the beginning of the climax. 



The second group of changes of the nuclear apparatus described 

 by Hertwig comprised: "Tiere mit vergrosserten Nebenkernen, 

 mit Sichelkernen mit 2, 4 und 8 Spindeln, Tiere, bei denen die 

 Teilung in die Haupt-und Nebenkernanlagen vollzogen war." 



From this brief note it is clear that the animals with two and 

 four spindles may possibly represent ordinary vegetative divi- 

 sion because the striking disintegration of the macronucleus is 

 not mentioned. We have never discovered an animal with eight 

 spindles, but ''Tiere, bei denen die Teilung in die Haupt-und 

 Nebenkernanlagen vollzogen war" are apparently identical with 

 those animals which we figure (figs. 21, 22, pi. 2) and represent 

 the important reconstruction of the new nuclear apparatus. 

 If it be true that in Hertwig 's culture conjugation had not oc- 



