60 RHODA ERDMANN AND LORANDE L. WOODRUFF 



shall in this paper confine ourselves chiefly to a descrij^tion of the 

 facts observed and to a ^'ery brief discussion of the theoretical 

 bearings, leaving for consideration at another time, when the 

 details of this reorganization process in other species of Protozoa 

 have been discovered, the more or less academic discussion, as 

 to the exact classification of this process among phenomena of 

 Entwicklungserregung. However, we may state at once, in 

 view of the somewhat premature criticism by R. Hertwig of 

 our work as presented by us in an avowedly preliminary ])aper 

 ('14, II), that we are convinced, after such a careful consideration 

 as any paper by Hertwig demands, that not a single objection 

 which he raises is well founded. We are also convinced that the 

 theoretical interpretations which Calkins ('15) advances in 

 regard to our results are not warranted by the facts so far at 

 hand. We take, then, in their entirety the facts and discussion 

 as presented in our complete paper ('14, III) as the starting 

 point for our present communication. 



II. MATERIAL AND METHODS 



The material used in the present study has been derived from 

 pedigreed races of Paramaecium caudatum which have been 

 bred in exactly the same way as described in our work on Para- 

 maecium aurelia, and the reader is again referred to that paper 

 for details ('14, III, p. 432). 



From our study of several races of Paramaecium caudatum 

 it seems clear that this species is less well adapted than Para- 

 maecium aurelia to withstand the conditions necessary for 

 pedigreed culture work. Whereas all the races of Paramaecium 

 aurelia which we have studied have survived indefinitely under 

 the daily isolation slide method of pedigreed culture manij^ju- 

 lation, most of the Paramaecium caudatum races ha\'c sooner 

 or later refused to divide under these conditions. As will be 

 discussed in detail later, the races on the slides can undergo the 

 reorganization, perhaps two or three times and then at the next 

 onset of the phenomenon, about 90 generations later, are unable 

 to carry it to proper completion and die. If, however, the 



