ANNULOIDA: ECHINODERMATA. 135 



ANNULOIDA. 



CHAPTER XVIII. 



i. GENERAL CHARACTERS OF THE ANNULOIDA. 2. GENERAL 

 CHARACTERS OF THE ECHINODERMATA. 



SUB-KINGDOM III. ANNULOIDA (^Echinozoa, Allman). This 

 sub-kingdom was proposed by Professor Huxley for the recep- 

 tion of the two groups of the Echinodermata and the Scolecida, 

 of which the former belonged to the old sub-kingdom Radiata; 

 whilst the latter was formerly classed with the Annulosa. The 

 same sections have been grouped by Professor Allman together, 

 under the name Echinozoa; the Rotifer a, however, being ex- 

 cluded from this division and classed with the Annulosa. By 

 others again, the Annuloida are looked upon as a section of the 

 Annulosa, and not as a distinct sub-kingdom. Provisionally, 

 however, it seems best to regard the Annuloida as one of the 

 primary divisions of the animal kingdom, it being impossible, 

 in the meanwhile, to frame a definition common to it and to 

 the Annulosa. The name Vermes has sometimes been em- 

 ployed to designate the sub-kingdom Annuloida, certain classes 

 being sometimes removed elsewhere, or certain others being 

 added. In its most modern signification, the term Vermes 

 may be held as synonymous with Annuloida, as here used, 

 plus the whole of the Anarthropodous division of the Annulosa. 



The Annuloida are distinguished by the presence of a distinct 

 nervous system, and the possession of an alimentary canal which is 

 entirely shut off from the general cavity of the body. A peculiar 

 system of canals, usually communicating with the exterior, and 

 termed the "water-vascular" or "aquiferous" system, is present 

 in all; and a true vascular apparatus is sometimes present. In 

 none is the body of the adult composed of definite segments, or 

 provided with "bilaterally disposed successive pairs of ap- 

 pendages" 



By Professor Allman the following definition has been given 

 of the Annuloida or Echinozoa : 



" Animals composed of numerous merosomes " (body-seg- 



