PROCESS OF REGENERATION 



117 



in the posterior zooid, so that a new gradient is estabUshed; this 

 gradient is of the primary type. If, therefore, a worm with a 

 well-developed posterior zooid is allowed to disintegrate in cyan- 

 ide, it is found to consist of two independent gradients; dis- 

 integration begins at the anterior end of each zooid, and proceeds 

 to the posterior end of each (fig. 12). There may be a shght 

 increased susceptibility at the posterior end of the first zooid. 

 After separation of the zooids, posterior growth sets in, producing 



S 15 <'> i-f ^.' -J.^ -'" 



Fig 11 Graph of the axial gradient of Dero limosa with a young zooid. 



again the rise in rate at the posterior end,whih is ccharacteristic 

 of Annelids. 



It is to be noted that it is the new anterior end and not the 

 new posterior end in which the marked rise in the rate of metab- 

 olism occurs. This change in rate is connected, first, with the 

 formation of a new head, and, secondly, with the reorganization 

 of the parts behind this head to form a new individual. The 

 visible changes in this latter process consist in the working over 

 of the anterior part of the intestine to form an oesophagus, and 

 of the circulatory system to form the 'hearts.' As a result of 

 these changes, the primary gradient is restored. 



