No. 6.] PROPORTIONATE STRUCTURES IN STENTOR. 321 



condition. Sooner or later a new ciliated band appears on 

 the old wall behind the part of the old peristome, as shown in 

 Fig. 4, > 2 . The band moves forward, fusing with the old ring 

 at one point and, replacing the latter, produces a new peristome. 

 Whether the piece of the old ring is entirely obliterated, or 

 whether a part of it remains to contribute to the new peristome, 

 I did not determine. The regeneration of a new peristome on 

 these pieces may be delayed for several days (Fig. 4, B^ ), and, 

 in general, does not appear as soon as on pieces that do not 

 contain any part of the old peristome. Five or six series of 

 experiments of this sort, each series of a number of pieces, 

 were made, and the smaller pieces followed with great care. 

 Only those smaller pieces were isolated that contained no part 

 of the old funnel. Nearly all the pieces behaved in the way 

 just described, but in one or two a small funnel developed 

 where the cut edges came together. This may have been due 

 to a very small piece of the original funnel having been cut off, 

 or to the piece having come from very near to the old funnel, 

 or, as seems more probable, to the development of a new funnel 

 from the old ciliated band. If the last interpretation is correct, 

 it shows that in exceptional cases the peristome may complete 

 itself. In the large majority of cases this does not occur and 

 a new peristome and funnel develop at the side and move 

 forward. In nearly all cases the cut ends of the old peristome 

 come together, meeting in a slight notch. In one or two 

 instances one band lay slightly below the other at the meeting 

 point, producing a peristome exactly like the normal in shape, 

 only the funnel was absent. If a small piece of the old funnel 

 is left, it assumes the characteristic position of the funnel, and, 

 in fact, becomes such to all appearance, although this peristome 

 is generally replaced later by a new one. 



Gruber studied the regeneration of pieces somewhat similar 

 to these without a funnel, and states that the remaining part 

 of the old peristome gives rise to a new one, but I have not 

 found this to be the case. If the piece is kept under close 

 observation, the development of a new peristome is found to 

 take place in the way just described. The change is sometimes 

 so rapid that a few hours may suffice to bring it about. 



