DYNAMICS OF MORPHOGENESIS 147 



the KCN on regulation in the first zooid is very shght and in the 

 posterior zooids the KCN increases the regulatory capacity ex- 

 cept in the ///pieces, where no morphological effect appears. In 

 series 512 the pieces were placed in KCN of higher concentration 

 as soon as cut and remained there for twenty-four hours. In 

 this series the effect of the KCN is a decrease in the regulatory 

 capacity in the first zooid and no change at all in the posterior 

 zooids. In general the effect of the KCN is different in the two 

 cases but the anterior and posterior zooids are clearly distinguish- 

 able in both by the difference in their dynamic condition. The 

 question as to why the different use of KCN gives such different 

 results will be considered elsewhere. 



Such series as these suflSce to distinguish the anterior zooid 

 from the group of posterior zooids, but they do not give any exact 

 information as to the number of posterior zooids or the position 

 of their boundaries. To obtain more definite results along this 

 line it is necessary to cut the region of the posterior zooids into 

 much shorter pieces: when this is done differences similar to 

 those between the first and second zooid in the above series though 

 less marked, appear between the other zooids composing the pos- 

 terior region: the anterior region of any zooid is in a different 

 condition from its posterior region and from the posterior region 

 of the zooid anterior to it. The only difficulty in the way of such 

 experiments is the variation in level of the boundaries between 

 zooids in different individuals. If for example, we cut the post- 

 pharyngeal regions of fifty worms 18 mm. in length into ten 

 pieces each and record the results for each lot of corresponding 

 pieces, we obtain only vague indications of the levels of the differ- 

 ent zooids because of the variations in level in different individ- 

 uals. If, on the other hand, we isolate each of the ten pieces from 

 each worm and record results we shall find that they are much 

 more definite for each individual and the variation in different 

 individuals becomes apparent. 



III. DISCUSSION 



The experiments described above indicate that the processes 

 concerned in morphogenesis, or at least some of them, differ in 



