PARALLEL PROCESSES OF MULTIPLICATION. 389 



m the indefiniteness of this organization, and in its want of 

 6xity. 



A further complication of the analogy is at hand. 

 From the aggregation of units into organized groups, we 

 pass to the multiplication of such groups, and their coales- 

 cence into compound groups. The Hydra^ when it has 

 reached a certain bulk, puts forth from its surface a tud, 

 which, growing and gradually assuming the form of the 

 parent, finally becomes detached ; and by this process of 

 gemmation, the creature peoples the adjacent water wath 

 others like itself. A parallel process is seen in the multipli- 

 cation of those lowly-organized tribes above described. 

 One of them having increased to a size that is either too 

 great for co-ordination under so rude a structure, or else 

 that is greater than the surrounding country can supply 

 with game and other wild food, there arises a tendency to 

 divide ; and as in such communities there are ever occur- 

 ring quarrels, jealousies, and other causes of division, there 

 soon comes an occasion on which a part of the tribe sepa- 

 rates under the leadership of some subordinate chief, and 

 migrates. This process being from time to time repeated, 

 an extensive region is at length occupied with numerous 

 separate tribes descended from a common ancestry. The 

 analogy by no means ends here. Though in the common 

 Hydra^ the young ones that bud out from the parent soon 

 become detached and independent ; yet throughout the 

 rest of the class Hydrozoa^ to which this creature belongs, 

 the like does not generally happen. The successive indi- 

 viduals thus developed continue attached ; give origin to 

 other such individuals which also continue attached ; and 

 60 there results a compound animal. As in the Hydra 

 itself, we find an aggregation of units wdiich, considered 

 separately, are akin to the lowest Protozoa ; so here, in a 

 Zoophyte^ we find an aggregation of such aggregations. 

 The like is also seen throughout the extensive family of 



