8IMILAKITY OF GROUPINGS. 3 Jl 



A further scries of changes begins now to take place ; to 

 which, as before, we shall find analogies in individual or 

 ganisms. Returning again to the Uydrozoa, we observe 

 that in the simplest of the compound forms, the connected 

 individuals developed from a common stock, are alike in 

 structure, and perform like functions : with the exception, 

 indeed, that here and there a bud, instead of developing 

 into a stomach, mouth, and tentacles, becomes an egg-sac. 

 But with the oceanic Ilydrozoa, this is by no means the 

 case. In the CalycophoridcB, some of the polypes growing 

 from the common germ, become developed and modified 

 into large, long, sack-like bodies, which by their rhythmi 

 cal contractions move through the water, dragging the 



o y oo o 



community of polypes after them. In the Physoplioridce, 

 a variety of organs similarly arise by transformation of the 

 budding polypes ; so that in creatures like the Physalia, 

 commonly known as the &quot; Portuguese Man-of-war,&quot; instead 

 of that tree-like group of similar individuals forming the 

 original type of the class, we have a complex mass of unlike 

 parts fulfilling unlike duties. As an individual Hydra may 

 be regarded as a group of Protozoa, which have become 

 partially metamorphosed into different organs ; so a Phy~ 

 salia is, morphologically considered, a group of Ilydrce of 

 which the individuals have been variously transformed to 

 lit them for various functions. 



This differentiation upon differentiation, is just what 

 takes place in the evolution of a civilized society. We ob 

 served how, in the small communities first formed, there 

 arises a certain simple political organization there is a 

 partial separation of classes having different duties. And 

 now we have to observe how, in a nation formed by the 

 fusion of such small communities, the several sections, at 

 first alike in structures and modes of activity, gradually 

 become unlike in both gradually become mutually-de* 

 pendent parts, diverse in their natures and functions. 



