78 THE EVOLUTION OF CONTINUITY 



into the lateral continuity of C. But it is to be noted 

 that this is cellular continuity, and that in C the cellular 

 discontinuity of A reappears as the discontinuity of the 

 cell-multiple or zooid ; and thus the next step in D is the 

 evolution of serial zooidal continuity. We might say that 

 as B is a cell-filament, so is D a zooidal filament. So it is 

 that we can recognise in the figure an alternation of Dis- 

 continuity with Continuity, as well as (in B, C, D) an 

 alternation of serial with lateral continuity. We shall see 

 that this alternation holds true for our next Continuity-type. 



It has already been put forward as a law that Con- 

 tinuity Produces Arrest ; and an outstanding feature of 

 Continuously Zooidal Individuals is zooidal arrest. As 

 the development of cells in serial continuity to make a filament 

 or " cell-colony " entails cell-arrest, so does the development 

 of zooids in series to form a zooidal colony entail zooidal arrest. 

 In the discontinuous Hydra, when one zooid has budded 

 another this is set free, and the gemmation area involved 

 may commence straightway to bud again ; but in the Con- 

 tinuously Zooidal Individual, when one zooid has budded 

 another the gemmation area involved is arrested for a con- 

 siderable time, and it may be permanently. For the budded 

 zooid remains attached, and it is by it that the next act of 

 gemmation is performed, after which arrest is again imposed 

 and further gemmation must come from the zooid last 

 produced. Thus, as regards a given series, the process 

 goes on till the end is reached with the production of a 

 sexual zooid. At the same time the phenomenon of release 

 from zooidal arrest is not uncommon, and a given gemmation 

 area may later give rise to a second zooidal series. Perhaps 

 the best examples of this are provided by flowering plants 

 and trees (whose derivation, it can be shown, is clearly 

 continuously zooidal, their special characters being the 

 result of change to an aerial environment). In these organ- 

 isms, where the stem or branch internode, or " segment," 

 represents the ancestral zooid, a given budding-area may 

 give rise to one branch only, or at considerable intervals of 

 time originate several others, especially if encouragement 

 is given by such procedures as pruning, heavy manuring, etc. 



Naturally, great variation in branching habit is exhibited 

 by existing Continuously Zooidal Individuals, but on the 



