ORAL AND APICAL SYSTEMS OF THE ECHINODERMS. 381 



this conclusion is the great resemhlance of the sculpturing 

 on the central disc of Marsupites to that on the subanal plate 

 of the young Salenia, as pointed out by Loven. This 

 sculpturing is found on all the plates of the calyx in many 

 of the Tessellate Crinoids^ and appears to be a primary 

 character. I do not think, therefore, that it would occur 

 on the central disc of 3Iarsupites, if the imperforate 

 nature of this plate were only due to a secondary calcareous 

 deposit, as must be the case if it be regarded as homologous 

 with the centrodorsal piece of Comatula. 



The following table has been drawn up to show the various 

 analyses which have been made of the apical system of 

 Marsupites and the other Crinoids, and the homologies in 

 the Echini of its various parts, as determined by Loven and 

 myself. 



There is one feature in the history of the Apical system 

 of the Crinoids which has an important bearing upon 

 Haeckel's celebrated worm theory of the Echinoderms. 

 This theory has been completely adopted by such a dis- 

 tinguished authority on the Echinoderms as G. O. Sars,i and 

 is supported by Gegenbaur~ in the last edition of his ' Com- 

 parative Anatomy,' while HaeckeP has quite recently spoken 

 of its truth as *' durch die Ontogenie und Palaontologie der 

 Echinodermen so schlagend bewiesen, dass jene altere 

 Auschauung ihr gegeniiber unhaltbar geworden ist." 



It appears to me, however, that the more we know of the 

 ontogeny and palaeontology of the Echinoderms, the greater 

 difficulties do we find in the acceptance of this theory, 

 according to which an Echinoderm is to be regarded as a 

 colony of " persons " which have arranged themselves in a 

 radiate manner around a common centre, somewhat in the 

 same way as the individuals forming a Botryllua colony. In 

 the latter case the individvals form for themselves a common 

 egestive aperture, while those forming a Starfish colony 

 have a common ingestive aperture, i.e. they are all united 

 together by their heads. For in the Asterids and Ophiurids 

 the first formed arm segment (ocular or radial) (fig. vii, 4) 

 is carried outwards and becomes the terminal plate of the 

 arm, corresponding to the tail end of an Annelid, while new 

 segments are added between it and the disc, according to 

 the usual laws of Annelid segmentation. In the Crinoids, 



^ "Researches on the Structure and Affinity of the genus Brisinga," 

 'Christiania University Program' for 1875, pp. 75 — 85. 



^ • Grundriss der Vergleichenden Anatomie,' ii Auflage, p. 205. 



^ " Ueber die Individualitat des Thierkorpers," ' Jenaische Zeitschrift, 

 Baud xii, p. 18. 



