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individuals (persons). Each of these is then, as it were, the individual which represents the 

 sexual generation, constructed according to the bilaterally symmetrical fundamental form, 

 and, as it were, most naturally referable to the class of Vermes. The so-called develop- 

 ment of the Echinoderms in the body of the larva, must then be considered as a sort of 

 budding of several worm-like individuals, which arrange, themselves radially round a common 

 centre, and, by concrescence of their oral extremities, form an individual of a higher order, 

 a colony or a complex of animals. A rather analogous case has already long been known 

 in the Salpse, in which similarly the 2 alternating generations represent morphological 

 individuals of different orders ; the non-sexual generation always consisting of single indi- 

 viduals (persons), which again, by budding, produce in their interior coherent complexes of 

 individuals . or colonies (the so-called Salpae-chains) representing the sexual generation. 

 If we examine the manner in which an arm or ray is reproduced de novo in an otherwise 

 developed star-fish, we shall similarly find cases which decidedly remind us of the Vermes. 

 The various joints or metamera are formed, as already noticed above, successively from the 

 base of the extreme first-formed joint, exactly in the same manner as the joints of a tape- 

 worm-chain, or like the segments of a nascent annelide. We come thus, in considering the 

 history of the development of the Echinoderms in general, to the same result to which the 

 minute investigation of the organisation in a fully developed star-fish has already led us. 

 The theory already set up by Duvernoy, afterwards developed in greater detail by Huxley, 

 and recently finally elucidated by Hackel, as to the composite individuality of the Echino- 

 derms and their phylogenetic connexion with the Vermes, — which theory was formerly 

 generally regarded as a wild fancy — must in reality, on more minute examination, be recog- 

 nised as having very much to support it; and so much the more, as we hereby obtain a 

 quite unexpected explanation of some hitherto very obscure cases in the natural history of 

 the Echinoderms. 



4. 

 On the genealogical relation of the several groups of Echinoderms to each oilier. 



We have above considered the proper star-fishes as the oldest, or original Echino- 

 derms, from which therefore all the other Echinoderms may be derived. We are led to 

 assume this in advance, quite simply by the fact that the star-fishes are, so far as we know, 

 of all the Echinoderms those which go furthest back in time, namely to the sub-silurian 

 formation. This assumption is also in the best harmony with the above-noticed theory of 

 the composite individuality and phylogenetic relations of the Echinoderms. If we consider 



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