In many cases the internal secretion is no mere accumulation, e.g. the internal skeleton of the Radiolaria, and the nematocysts of the Coelentera.

These three sets of structures, with the funnel from which they rise, make up the endodermal coelenteron, or gastro-vascular system.

Such forms he distinguished as Coelentera, and showed that they had no special affinity with echinoderms, polyzoa, &c.