Role of Preformed Structure in Cell Heredity 185 



bule, mouth, gullet, and the typical circumoral kinety field, hut 

 possesses all other structural features of an oral segment, i.e., the 

 preoral suture with its right and left kinety fields and the postoral 

 suture with its cytopyge and right and left kinety fields. Between the 

 complete and incomplete oral segments are two ahoral surfaces also 



FIG. 9. Doublet lacking vestibule, mouth, and gullet of one oral meridian, but 

 retaining rest of the meridian. Two focal levels of silver preparations of same cell. 

 A. Surface with incomplete oral meridian at upper focal level. B. Surface with 

 complete oral meridian at lower focal level. (As before, the animal's right and left 

 are the same as the observer's on the lower surface but are reversed on the upper 

 surface.) al, anterior left kinety field; ar, anterior right kinety field; m, mouth; pi, 

 posterior left kinety field; pr, posterior right kinety field; py, cytopyge; s, preoral 

 suture; *, area where vestibule, mouth, and gullet are missing. 



180° apart, each with its segment hearing contractile vacuole pores. 

 This incomplete doublet, lacking only the middle parts of one oral 

 segment, reproduces true to type. Clearly, the smallest autonomous 

 cortical part is less than an entire normal interpolar segment. 



A number of other hereditary cortical variations have been ob- 

 tained: triplets, quadruplets, a much increased number of contractile 



