THE MORPHOLOGICAL COMPOSITION OF ANIMALS. 85 



vision of the Coelenterata, known as the Actinozoa. Here, too, 

 we have a group of species — the Sea-anemonies — the individ- 

 uals of which are solitary. Here, too, we have agamogenetic 

 multiplication: occasionally by gemmation, but more fre- 

 quently 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 Coelenterata 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 in- 

 tegrations will insensibly arise, if the separation of the gem- 

 miparous 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. 



§ 203. The like relations exist, and imply that the like 

 processes have been gone through, among those more highly- 

 organized animals called Molluscoida. We have solitary 

 individuals, and we have variously-integrated groups of indi- 

 viduals : the chief difference between the evidence here fur- 

 nished, and that furnished in the last case, being the absence 

 of a type obviously linking the solitary state with the aggre- 

 gated state. 



It is now an accepted belief that the creatures named Braclii- 

 qpoda, very abundant in the so-called palaeozoic times, but at 

 present comparatively rare, are akin in structure to the 

 Polyzoa ; widely as they differ from them in size. If we can- 

 not fairly say that by union of many Brachiopods there would 

 be produced a compound animal like a Polyzoon; yet we may 

 fairly say that were a small imperfectly- developed Brachiopod 

 united with others like itself, a Polyzoon would result. This in- 

 tegration of aggregates of the second order, is carried on among 



