PROCESS OF REGENERATION 



i09 



of death about coincides with that of the principal zooid; but, 

 owing to the processes of dedifferentiation and growth involved 

 in its formation, its susceptibility to cyanide continually increases 

 so that its death comes to preceded by a considerable time inter- 

 val that of the principal zooid. The rate of metabolism of the 

 zooid thus continuously rises during its development. 



Eventually the presence of the posterior zooid is made known 

 through the appearance of a fission plane, and its structural 



Fig. 5 Graph of an Aeolosoma with a zooid well diflferentiated morphologi- 

 cally, showing the two independent gradients that of the zooid being at a higher 

 level. 



differentiation proceeds. If examined in cyanide at this time, 

 the two independent gradients show very clearly, that of the 

 posterior zooid being at a higher level (fig. 5) . The axial gradient 

 of the posterior zooid is of the primary type, and remains so, 

 indeed, until it has separated from the parent animal and begun 

 to produce zooids of its own. The gradient of the anterior zooid 

 is at the beginning of the development of the posterior zooid 

 also of the primary kind but later becomes altered. Disinte- 

 gration starts at its head and proceeds posteriorly, but soon the 



