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2. 



Of the fundamental form of the Echinoderms and of their morphological individuality as illustrated 



in the genus Brisinga. 



As is well known, Cuvier referred the Zoophytes and Echinoderms to one and the 

 same animal type, the so-called radiates; and he has been also followed in this respect by 

 the American naturalist (Agassiz) while here in Europe. We have generally adopted the 

 views first developed by Leuckart, according to which both these groups are sharply distin- 

 guished from each other as belonging to essentially different original types. It was the 

 radiary primitive form presumed to be common to both groups, which Cuvier laid so much 

 stress on; and the American naturalists have also held this characteristic to be of such pro- 

 minent importance, that they still consider the Zoophytes and the Echinoderms, in spite of 

 the many essential differences in their organisation, as belonging to one and the same ani- 

 mal type. If however we follow the method of investigation above indicated, according to 

 which we must take the Asterides, and among these especially the genus Brisinga, as the 

 most original or least changed form of star-fish, for our type, and from this point of view 

 institute our comparison between the Zoophytes and the Echinoderms, we shall find that 

 in reality there is a very essential difference between the strictly radiary structure of the 

 former and the so-called radiary structure in the star-fish, a difference which is of so vital 

 importance that we cannot do otherwise than reopen the question which might seem to 

 have been settled long ago, namely whether the Echinoderms, when all is considered, can 

 be held to be real radiates in the same sense as the Zoophytes. If we now examine the 

 so-called rays or arms in the proper star-fishes, from which again all the other Echinoderms 

 may naturally be derived, we shall find at first that they exhibit a far greater self-sufficiency, 

 a far more self-contained organisation than we ever can find in the Zoophytes, a fact which 

 in the Brisinga is more prominently evident than in any of the other known Echinoderms. 

 While in other Asterides there is always found a more or less strongly developed central 

 section or disc, this is in the Brisinga so extraordinarily reduced, that the whole body may 

 be said to consist of a certain number of arms connected at the base. If we further con- 

 sider a ray or arm of a star-fish by itself, we shall find that besides exhibiting a perfect 

 bilateral symmetry, it consists of a series of consecutive joints or sections (metamera), a 

 division which is not only expressed in the ambulacral skeleton, but also in most of the 

 other organic systems. If we as formerly, consider the arms of the star-fishes to be real 

 corresponding parts (antimera) analogous to the antimera of Zoophytes, we come to the 

 paradoxical result that an antimeron can be composed of metamera, which according to 

 Hiickel l is the next highest order of individuality. On the other hand the matter is explained 



1 Generelle Morphologic der Organismen. 



10* 



