Role of Preformed Structure in Cell Heredity 181 



tical parts be reproduced in the progeny? Would deleted cortical parts 

 be regenerated, or would the progeny also lack them? Answers to 

 these questions, together with the results of the breeding analysis set 

 forth above, should leave no doubt as to whether genetic autonomy is 

 possessed by the cell cortex and its parts. 



The difficulty in trying to answer these questions in Paramecium is 

 that this organism has thus far seemed to be a poor material for the 

 needed sort of operations. Although the body can be cut in various 

 ways, removal of cortical parts alone has met with little or no success 

 and grafting has never succeeded. However, as has so often happened 

 in the past, paramecia themselves frequently accomplish what the 

 experimenter is unable to do. In effect, they themselves performed 

 grafting operations and brought about losses of cortical parts. 



In two instances following conjugation, a paramecium grafted onto 

 itself a piece of cortex from its mate. The first case (Fig. 7) was of 

 course the most exciting one. A doublet .mating with two singlets was 

 briefly exposed to immobilizing antiserum in order to induce cyto- 

 plasmic bridge formation (Fig. 1A). The doublet never separated 

 from one of the singlets; the other singlet, however, separated except 

 for the induced cytoplasmic bridge (Fig. IB). The singlet remained 

 long united to the doublet, but eventually separated (Fig. 1C). The 

 doublet and its still-attached other singlet mate eventually died, but 

 the free singlet lived. When first observed after separation, it bore 

 a very conspicuous extra piece, as shown in Fig. 1C. Its doublet mate 

 at that time showed a corresponding nick, as if a piece were missing. 

 The singlet, in breaking away from the doublet, had apparently taken 

 along a piece of the doublet's cortex. Instead of growing rapidly and 

 dividing within about 11 hours, as is normal for exconjugants, this 

 singlet failed to grow for two days. During that period, its extra piece 

 flattened out, making the posterior part of the body distinctly wider 

 (Fig. ID). Then the abnormal animal grew and reproduced (Fig. 

 IE). From one I but not the other) of the two products of the first 

 fission arose a clone obviously different in form from either singlets 

 or doublets ( Fig. IF I . When samples of this clone were observed, 

 after preparation by the silver impregnation technique, we found to 

 our amazement and delight a new hereditary type that went far toward 

 answering our question about the autonomy of cortical parts. 



These animals (Fig. 8) were intermediates between singlets and 

 doublets. Like doublets, they had two complete oral segments: two 

 vestibules, mouths, and gullets; two anterior and posterior sutures; 

 usually two cytopyges; and two sets of the five typical associated 

 kinety fields ( anterior right and left, circumoral, and posterior right 



