DYNAMICS OF MORPHOGENESIS 143 



tion within the limits of a single zooid, but also a marked change 

 between the first and the second zooids. 



Many other series have been carried through with KCN, with 

 alcohol and with low temperature and in all the region of the 

 second zooid differs in its reaction to the experimental factor 

 from the posterior region of the first zooid. 



2. Some further cyanide experiments: the relation between inethod 



and results 



It must not be supposed that a given experimental factor always 

 produces the same results on animals or pieces which are in the 

 same physiological condition. The character of the result depends 

 to a large extent upon the method in which the experimental fac- 

 tor is used. Two series are presented to illustrate this point: 

 in both the differences between first and second zooids appear, 

 but they appear in a different way because the KCN is used differ- 

 ently in the two series. These series and many others essentially 

 similar to them constitute further evidence in support of the 

 dynamic character of the axial factor. All that was said above 

 (p. 136) concerning the size of the worms, their feeding, etc., 

 applies to the two following series as well. 



Series 512 I and III. March 5 to 18, 1912. In this series KCN 

 Toi-so ro.- acting during the first twenty-four hours after the pieces 

 were cut, is the experimental factor used. The whole length of 

 the worms except the head was cut into six pieces as nearly as 

 possible equal in length, as indicated on the right side of figure 46. 

 Of these pieces a and b included most of the first zooid, while c 

 consisted of the posterior region of the first and the anterior region 

 of the second zooid and d, e and/ were parts of the posterior zooids, 

 / corresponding more or less closely to the most posterior zooid 

 or the 'growing tip' (Child, '11 f): each piece is then somewhat 

 longer than the pieces in the two series of the preceding section 

 and the c-pieces include parts of both the first and second zooids. 



Lots of fifty each of these six pieces were placed in water at 

 room temperature as a control. Similar lots, but of forty each 

 instead of fiftv — the stock from which these worms were taken 



