74 



a wider range; and we come also to a very different result with respect to the relation of 

 the genus Brisiuga to the other Echinoderms. With Darwin's doctrine in view, we can not 

 imagine the type of Echinoderms as anything perfectly defined and given from the very 

 first; but we must imagine this type, like the other higher animal types, as having been 

 produced through successive divergent developments of lower animal forms. We have there- 

 fore first and foremost to examine the relation in which the type of Echinoderms stands 

 to the lower animal forms known to us, and seek to discover which of these may be con- 

 sidered as the starting point for the series of developments observed in the Echinoderms. 

 To settle this important point, it is first expedient to decide which of the now living Echi- 

 noderm-forms may be presumed to have undergone the least change, and therefore may be 

 considered as the oldest or the most original forms. For the solution of this question 

 Pakeontology will naturally furnish the most important data. The fii'St Echinoderms which 

 occur, are those in which we may expect to find the phylogenetic origin of the type best 

 illustrated. For a long time it has been supposed that the Crinoida; or stone-lillies were 

 the oldest Echinoderms, and especially the so-called Cystidea which already appeared in 

 great number in the palaeolithic time. It appears however on more recent examination, that 

 the Asterides are of still much greater antiquity, for which reason we may also consider 

 this group of Echinoderms as the eldest, from which all the other groups of Echinoderms 

 have been developed. Of the now living Asterida;, those forms may be considered as the 

 eldest or least changed, which in their habitus agree most with the first forms of remote 

 antiquity. This is now precisely the case with the Brisinga, in a greater degree than with 

 any of the other known star-fishes. 



Its habitual resemblance to the oldest known star-fish Protaster is unmistakable; 

 and Asbjornsen has already drawn attention to this important point. Several other circum- 

 stances will now confirm us in the opinion that we have before us in the Brisinga a very 

 ancient form, an isolated surviving representative of the Echinoderms of primitive times, 

 which, confined to the great depths of the ocean, where the physical circumstances have 

 been in all times somewhat similar, has managed in undistiu'bed peace to preserve the 

 original structure, without requiring to keep pace with the remarkably extensive transfor- 

 mation and diversity of development observed in the Echinoderms generally, and specially 

 in the Asterides. Now the Asterides being, as already stated, considered as the oldest 

 race of Echinoderms, from which the other types of Echinoderms have only been ramified 

 in later times, the genus Brisinga acquires a double importance, as the starting point for a 

 correct appreciation of the nature of the Echinoderms and of their relation to other ani- 

 mal types. 



