REGENERATION 127 



plasmic striping grew out and the normal form and proportions 

 of a stentor were reconstituted on a small scale. But nothing of 

 this happened if no nuclear beads were included and the fragment 

 then remained until death about four days later just as it was after 

 cutting and healing. It would therefore seem that the nucleus is 

 essential in both the formation and the dedifferentiation of oral 

 structures. These cases demonstrate how capable is Stentor in 

 adjusting its parts to normal proportions. 



Fig. 32. Adjustment of size of parts in nucleated, isolated head 

 of S. coeruleus. Feeding organelles and frontal field are excised 

 without injury but with minimum lateral ectoplasm. In folding 

 to cover the wound the fragment becomes much contorted. 

 Membranellar band decreases in length and lateral striping 

 gradually grows out to form a tail-pole. Later the mouthparts 

 are also decreased in proportion. Adjustment occurs without 

 primordium formation but only if nucleus is present. 



7. Can mouthparts and membranelles be formed in situ ? 



In the normal course of life new feeding organelles in Stentor 

 are formed only through the development of an oral primordium ; 

 yet there are hints in the literature that this may not be the only 

 pathway to oral differentiation, although no really convincing 

 demonstrations have been offered. In respect to the mouthparts, 



D. Primordium sector isolated from a stage-4 regenerator. 

 Development continues and size of mouthparts is proportionate 

 not to the original cell or the length of the anlage but to the size 



of the fragment. 



E. Tail pole was grafted to frontal field of a stage-2 regenera- 

 tor. First sketch shows an additional anlage now induced in the 

 graft. On developing, the primordia produced mouthparts 



proportionate to the size of the part in which they arose. 



