No. 6.] PROPORTIONATE STRUCTURES /A" STl-:.\ /'< >A\ 317 



Fig. 3, f> 1 . After three days more the new stentor had about 

 the same form. The peristome is, as compared to that of the 

 original stentor, too wide for the length of the new individual, 

 although it is not much more than half the width of the old 

 peristome. 



The development of the posterior piece is shown in Fig. 3, 

 C l and 7 2 . In this piece, particularly in the earlier stage, C l , 

 the peristome is smaller than was the original peristome, ami 

 also relatively smaller as compared with the entire length of 

 the animal. 



In order to be certain that the anterior pieces did not pro- 

 duce new peristomes during the night, they were kept in a 

 cold place when not under observation ; for I had found that 

 under these circumstances the formation of a new peristome is 

 greatly delayed, even although it may have begun to develop 

 before the piece is subjected to the cold. In this way I could 

 retard the development of the peristome for twelve hours, so 

 that I felt certain that a new peristome had not developed on 

 these anterior pieces in my absence. 



In other experiments pieces of different sizes were cut from 

 the foot-end in order to see if the size of the new peristome 

 that is formed is in proportion to the size of the piece. It was 

 found that a smaller peristome develops on a smaller piece, and 

 a larger one on a larger piece; and this same relation holds 

 also for pieces of different sizes for other parts of the body. 

 It has been shown that cross-pieces from the anterior or 

 posterior ends retain some of their original peculiarities even 

 after the formation of a new individual, and that for several 

 days the stentors from anterior pieces are too broad for their 

 length, and individuals from the posterior end are too long for 

 their breadth. Some of these newly regenerated stentors from 

 the anterior pieces were kept for a longer period and supplied 

 with food. Their measurements for from one to seventeen 

 days after the operation are given in the following table. 

 The measurements of three normal individuals of this lot 

 were 1.6 x .5 ; 1.4 x .4 ; 1.1 x .4. The experiment began 

 February 3. 



