ORGANIC STRUCTURE : MORPHOLOGICAL 41 



Thus we may cut across the Unes of a rational classification 

 and consider such other life-types as the following : 



iim. Colonial Types. (See Section 11/. "Colonies" of 

 Hydrozoa or Polyzoa are, we have suggested, integrations of 

 segmental parts. (" Integrations of the second order," Section 

 loh.) The "joints" of a worm, or lobster, for instance, are 

 segments integrated into a body acting as a unity. So are the 

 " arms " of a starfish. So also the zooids of an Antennularian, 

 or of a Polyzoan are best regarded as segments with a very im- 

 perfect degree of integration (but in a Siphonophore the integra- 

 tion of the zooids is much more complete). Loosely, and from 

 long usage, such Hydrozoan, Siphonophore, Polyzoan, etc., 

 aggregates are called " Colonies." 



Colonies of worms, of Salpidas, etc., are rather diff^erent from 

 the Ccelenterate and Polyzoan colonies. In the former the units 

 that cohere, or associate, are already pluri-segmental animals. 

 Here, then, in such latter colonies we have rather communities 

 in which the integration is not merely the result of the combined 

 behaviours of the units (as in a bee-hive) but there is actually 

 structural adhesion of the units of a colony (as in the worm- 

 groups, Sahella, or in a chain of Salpidas). We might, perhaps, 

 speak of such associations as " integrations of the third order " : 

 communities in which the nexus is structural rather than be- 

 haviouristic as in, say, the gregarious herd. 



iiw. Motile, Sedentary and Sessile Types. Motility of 

 the animal is universally the case, at some phase, or throughout 

 the individual life-history. The animal organism is, in general, 

 able to move about and many species are characterized by very 

 definite, seasoned migrations which they perform. Even if the 

 adult animal is not motile its eggs or larvae have powers of move- 

 ment, or they are dispersed by being carried by water currents. 

 This motility, or dispersal of the ova or larvae ensures the distribu- 

 tion of the species over a wide region. There are sedentary 

 animals (Mussels, Oysters, etc.) which throughout their adult 

 lives do not move far from the places on the sea-bottom to which 

 they are more or less rigidly adherent. There are truly sessile, 

 " rooted " types, such as the Sponges, Zoophytes and Polyzoa 

 which are attached permanently to the sea-bottom. Sedentary, 

 semi-sedentary and sessile animals always have eggs and larvae 

 that are motile, or undergo dispersal. With the assumption of 



