Growth, Regeneration, Cell Recognition, Perspective on Cell Differentiation

Abstract

The subject of sponge development is especially complex due to the multiplicity of systems capable of establishing a functional animal. The following, naturally occurring processes are known to lead to the development of a animal possessing a functional canal system: larval metamorphosis, the differentiation of regressed tissue, budding, and the hatching of gemmules. These processes result in the formation of a new (but morphologically immature), functional animal and have been treated in earlier chapters (Chaps. 7, 8). In addition to them, four aspects of growth can be recognized; one of which (initiative growth) can lead to the establishment of a number of additional canal system units in the same animal and consequently to what has been classically referred to as colonialism (Hartman and Reiswig, 1973; Simpson, 1973). Finally, studies of experimental regeneration, encompassing questions of cell recognition, can be separately treated and involve the manipulation of adult tissue including the reaggregation of dissociated cells, explantation (cuttings), transplantation (grafting) of tissue, parabiosis and tissue ablation.