330 ABSTRACTS OF PAPERS. [VOL. II. 



do not regenerate, but if a small portion of the entodermal 

 digestive sac be present regeneration is complete, provided 

 the piece is above a certain size. 



If a chain be artificially separated into its zooids before they 

 have attained their full development, each zooid undergoes a 

 form-regulation, assuming within a few hours what may be 

 called the normal proportions, i.e., the length becomes eight 

 or ten times the transverse diameter. This regulation does 

 not occur while the individual is a zooid in a chain, because 

 the whole chain is not simply a series of individuals, but in 

 some degree a single individual, and therefore possesses cer- 

 tain proportions differing from those which each zooid would 

 possess if single. 



When the chain is cut at various points between the zones 

 of fission, the results differ according to the degree of develop- 

 ment of the particular zone of fission concerned and the parts 

 adjoining it. If a piece containing a very young septum be 

 cut out from a chain, the septum disappears and a single 

 perfect individual is formed from the parts, which originally 

 belonged to two different zooids. A head is regenerated at 

 the anterior cut surface, a tail at the posterior end. If the 

 included septum be more fully developed, it remains, and 

 the part anterior to it is completely absorbed by the part 

 posterior to it, the head of the new individual resulting being 

 the head which was forming just posterior to the septum. 

 The relative size of the parts anterior and posterior to the 

 septum does not affect the result, unless the posterior piece 

 be very small. It is always the anterior part which is 

 absorbed, never the posterior. If the septum be still more 

 advanced in development, the portion anterior to it is only 

 partly absorbed. It regenerates a new head and becomes a 

 perfect zooid, though at first it decreases in size, owing to the 

 partial absorption. 



In general each zooid tends to absorb material from the 

 zooid anterior to it. Each zooid, however, offers a certain 

 resistance to this absorption, the resistance increasing as it 

 approaches the condition of independent individuality. When 

 the individuality of a zooid is destroyed or reduced to a lower 



