Coordination in Sponges. The Foundations of Integration

Coordination mechanisms in sponges involve not only epitheliabut also the mesenchyne, which is the basic internal milieufor aii primitive Metazoa. There are three main types of coordination pathways: (i) Fluidextracellular coordination pathways are used for the spreadingof materials through the mesenchymal connective matrix. Examplesare provided by the processes of wound healing, regeneration,gametogenesis, and gemmulation. (ii) Mobile cellular coordinationpathways follow the transitory contacts and consecutive exchangesperformed by amoeboid cells which wander in the mesenchymalmatrix. Examples are provided by the processes of cell reaggregationand morphogenesis, (iii) Fixed tissue coordination pathwaysare achieved by permanent connections between cells belongingto the same unit structure, which can be an epithelium or whichcan be composed of mesenchymal cell networks and bundles. Examplesare provided by contractile activities of oscular membranes,internal canals, or of the whole sponge. The first and the secondpathways do not undergo significant modifications in the variousspecies of sponges. The third pathway, and especially the mesenchymalcontractile tissue, appears to be significantly well developedonly in thick-walled sponges. The discussion compares the three coordination systems of spongeswith integrative systems in higher Metazoa. The conclusion isthat if the coordination mechanisms in Porifera do not quiteresemble those found in higher animals, nevertheless they wouldhave been suitable for a further advent of true hormonal, immune,muscle, and nervous systems such as we know in other Metazoa.     

The Cellular Basis for Colony Form in Podocoryne carnea

During the past 10 years considerable data have appeared indicatingthat the growth of hydroids is not, as was earlier believed,similar to the meristematic growth of plants, but rather thatthe sites of cell proliferation are removed in space from thesites of utilization, that cells migrate individually, activelyas amoebocytes through the epidermis or pawively as epitheliocytescarried along in the hydroplasm, to the sites of utilization,and that considerable migration across the mesoglea occurs. A model of hydroid morphogenesis and morphostasis based on thisnew information provides a comprehensive picture, albeit onefilled in with numerous assumptions, of the manner in whichcolony form is produced as a consequence of cell proclivities.