A parallel series of illustrations might be drawn from that second division of the _Cœlenterata_, known as the _Actinozoa_. Here, too, we have a group of species--the Sea-anemones--the individuals of which are solitary. Here, too, we have agamogenetic multiplication: occasionally by gemmation, but more frequently by that modified process called spontaneous fission. And here, too, we have compound forms resulting from the arrest of this spontaneous fission before it is complete. To give examples is needless; since they would but show, in more varied ways, the truth already made sufficiently clear, that the compound _Cœlenterata_ are aggregates of the third order, produced by integration of aggregates of the second order such as we have in the _Hydra_. As before, it is manifest that on the hypothesis of evolution, these higher integrations will insensibly arise, if the separation of the gemmiparous polypes is longer and longer postponed; and that an increasing postponement will result by survival of the fittest, if it profits the group of individuals to remain united instead of dispersing.[19] § 203. The like relations exist, and imply that the like processes have been gone through, among those more highly organized animals called _Polyzoa_ and _Tunicata_. We have solitary individuals, and we have variously-integrated groups of individuals: the chief difference between the evidence here furnished, and that furnished in the last case, being the absence of a type obviously linking the solitary state with the aggregated state. [Illustration: Figs. 153–155.] This integration of aggregates of the second order, is carried on among the _Polyzoa_ in divers ways, and with different degrees of completeness. The little patches of minute cells, shown as magnified in Fig. 153, so common on the fronds of sea-weeds and the surfaces of rocks at low-water mark, display little beyond mechanical combination. The adjacent individuals, though severally originated by gemmation from the same germ, have but little physiological dependence. In kindred kinds, however, as shown in Figs. 154 and 155, one of which is a magnified portion of the other, the integration is somewhat greater: the co-operation of the united individuals being shown in the production of those tubular branches which form their common support, and establish among them a more decided community of nutrition. [Illustration: Figs. 156–159.]