The findings presented here have a bearing on regeneration in general. They show that even in simply organized animals, the number of totipotent cells which are able to differentiate decreases as the individual ages. In older specimens it takes longer for the totipotent cells to differentiate than in younger ones; at the same time the nuclear and cytoplasmic volume of these cells is reduced.

The expanded basal epithelium of sponges germinating from gemmules is an organ necessary to establish the tension in the body which is indispensable for the functioning of the sponge. Sponges that have germinated from gemmules can be forced to regenerate a basal epithelium. The materials for this regeneration is furnished by the archaeocytes, which are embryonic, totipotent amoebocytes. The number of archaeocytes that are able to perform this regeneration decreases with time, i.e. as the differentiation of the entire body proceeds.

On the other hand, the ability of the sponge to expand repeatedly on its own basal epithelium after being pushed away from it is limited only by the onset of cytolysis.

The ability of the archaeocytes to regenerate new typical basal epithelial cells is reduced after repeated regeneration.

The size of both nucleus and cytoplasm is reduced more and more during repeated regeneration. The nucleo-cytoplasmic ratio is thus kept fairly constant.

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