78 



3. 



On the phylogenetic relationship of the Echinoderms to other animal types. 



If we accept the theory noticed in the preceding paragraph with respect to the compo- 

 site individuality of the Echinoderms for which, as will be shewn, the examination of the Bri- 

 singa seems to afford essential support, we shall quite naturally come to judge of the generic 

 relationship of the Echinoderms to other animal types in a very different manner from here- 

 tofore. We thus see in' the star-fishes the most original and least altered Echinoderms, which 

 therefore must be selected as the starting point for our comparison with other animal types. 

 Moreover it is not the whole body of the star-fish, but the single rays or arms which must 

 here form the subject of our investigations; as these rays or arms do properly represent the 

 original echinoderm individuals or persons. We have in the first place before us a comple- 

 tely bilaterally symmetrical body, with a dorsal and a ventral side, right and left side, oral 

 and aboral extremity, the interior organs of which shew the same strict symmetry. Next 

 we shall find that these internal organs have a fixed regular and peculiar position relatively 

 to each other: below, the central parts of the nervous system; then, the vascular system 

 with the parts appertaining to it; then, the perivisceral cavity with the digestive system and 

 organs of generation contained therein; and externally, the skin, consisting of 2 distinct 

 layers, the interior muscular, and the exterior cellular. We find moreover that this body 

 exhibits a series of consecutive similar sections or metamera, not only expressed in the 

 skeleton but also in several of the interior organic systems: the muscular system, the 

 nervous system, the vascular system. These are 'all things which we only find again in 

 the great race of the articulata and particularly in the worms (Vermes). We are naturally 

 led hereby to the conclusion that the nearest relations of the Echinoderms are not. as 

 hitherto generally supposed, the Zoophytes, but the Vermes; and that this last ancient and 

 extensively ramified trunk, in which we trace, as it were, the very first rough sketches of 

 all the higher animal types (even including the vertebrata) must also be regarded as the 

 trunk from which the Echinoderms, although apparently of a very different fundamental 

 structure, have had their origin. This theory of the phylogenetic development of the Echi- 

 noderms, which is likewise most sharply and most clearly represented by Hackel, acquires 

 also an essential support from the Brisinga, the so-called rays or arms of which exhibit 

 more evidently than in any other Echinoderm a worm-like appearance, and the great self- 

 sufficiency of which is not only expressed in the exterior, but also in the interior organi- 

 sation; for, as has been already observed, even the organs of generation, which else, at least 

 in great part, are confined to the central section or disc, are here entirely separated from 

 the same, and symmetrically imbedded in the cavity of the arms. The relationship of the 

 Echinoderms to the Vermes has indeed long ago been recognised by some naturalists; 



