85 



branches (Pinnulse); of both these sorts of ramification we have instances in the Crinoids, 

 and of an extremely extensive dichotomic splitting in the Euryalse. In these last the arms 

 may be said to have attained a stronger development in this direction than in any other 

 Echinoderm. Nevertheless such a Euryala with its widely ramified arms, the mass of which 

 surpasses many times the mass of the disc, is far more centralised than even the most 

 short-armed star-fishes. As regards the fossil groups Blastoidea and Cystidea these, are 

 most nearly related, as divergent branches, to the Crinoids. The arms have here apparently 

 undergone, by some peculiar processes of adaptation, a retrograde development. We may 

 perhaps so far most properly consider them as degenerate Crinoids, just as the footless 

 sea- cucumbers (Synapta) may be supposed to be degenerate Holothurians. 



The genealogical relationship of the various groups of Echinoderms to each other 

 may henceforth, with special r,egard to the various modes of centralisation of the cormus, 

 be graphically represented as follows: 



Centralisation by continued concrescence with reduction of the antiambulacral area. 



Centralisation without 

 continued concrescence, with special 

 development of the antiambu- 

 lacral area. 



I 



(Pentacta) 



Holothurida 



(Eupoda). 



Centralisation without 



continued concrescense, with special 



development of the arms. 



Antedon. 

 (Pentacrinus). 



(Palseechinns). 



Euryalae. 

 (Amphiura). 



C r i n o i d a . 



(Articulata). 

 (Archasterias?). 



E c h i n i d a . 



(Dermostichaj. 



(Asterias). 



O p h i u r i d a , 

 (Ophiura). 

 (Protaster). 



A s te r i d a. 

 (Brisinga). 



Colony-forming 

 Vermes. 



5. 



Of the relation of the genus Brisinga lo the Asleroidea in general. 



After having made the above more general remarks on the organisation of the Echi- 

 noderms and their relationship to other animal types, as exemplified in the genus Brisinga, 



