Role of Preformed Structure in Cell Heredity 207 



production at the narrow- and fine-stripe juncture in Stentor (Tartar, 

 1961). These ohservations appear to indicate that the interactions in 

 hotli cases are due to an inductive influence from the one region 

 (wide-striped in Stentor) which spreads hoth to the right and to the 

 left. Normally, only the region on one side is competent to respond in 

 hoth cases; hut when competent regions are on hoth sides at once, 

 hoth sides respond concurrently. That a competent responding area 

 must he present for the response to occur is shown hy the normal 

 limitation of the response to one side. So far as I am aware, present 

 knowledge of the cytopyge does not permit a choice as to whether the 

 left kinety area is the inductor and the right the competent responder, 

 or the reverse. Perhaps the discovery of induction at the juncture, 

 even when the juncture is not on an oral meridian and when the 

 right-left relations are reversed, will inspire successful efforts to re- 

 solve the remaining questions. 



With regard to the possihle morphogenetic role of the cortical pat- 

 tern juncture hetween vestihule and gullet in Paramecium, resolution 

 of the alternative interpretations is rendered especially difficult. The 

 position where the anlage of the new oral apparatus is first seen is 

 very close hoth to the endoral (stomatogenic? ) kinety and to the 

 juncture of the strongly marked differences in cortical pattern. At- 

 tempts to test which of these structural landmarks, if either, is decisive 

 for the appearance of the anlage of a new oral apparatus could follow 

 either of two paths. First, the earliest beginning of the anlage could 

 be studied to see if it is in fact physically contiguous with the endoral 

 kinety. Rocpie ( 1956b ) and Porter ( 1960 ) , using the silver method, 

 claim that it is; Ehret and Powers (1959), using phase and electron 

 microscopy, claim that it arises several microns from this region. 



Second, attempts might he made to separate the endoral kinety 

 from the vestibule-gullet juncture. This would not be easy, perhaps 

 not possible, to do surgically: however, repetitions of certain experi- 

 ments, plus cytological controls, might accomplish the task. One such 

 experiment was Hanson's (1955) destruction of the ability to form 

 a gullet on one oral meridian of a doublet by exposing the area of 

 the right posterior vestibule-gullet juncture on that meridian to a 

 fine beam of ultraviolet irradiation. Cytological study accompanying 

 such an experiment should reveal whether certain structures such as 

 the endoral kinety were destroyed. Hanson did not have cytological 

 controls and did not even know whether the rest of the oral meridian 

 persisted in progeny that lacked one vestibule, mouth, and gullet. 

 Perhaps they were like our incomplete doublets that had this oral 

 segment except for vestibule, mouth, and gullet. Another type of 



