THE ANNTJLOIDA AND ODONTOPHORA. 81 



similarity. Each is a system of canals, opening externally, and 

 ciliated within ; and the circumstance that the two apparatuses 

 are turned to different purposes in two distinct groups of the 

 animal kingdom, seems to me no more to militate against their 

 homology, than the respiratory function of the limbs of the Phyl- 

 lopod Crustacea militates against the homology of these limbs 

 with the purely locomotive appendages of other Crustaceans. 



Thus it appears that the Echinodermata and the Scolecida 

 are so closely connected that they can by no means be placed 

 in separate sub-kingdoms; and, in the course of studying the 

 other sub-kingdoms, it will be quite obvious that, unless they 

 are to occupy an independent position, there is no place for 

 them anywhere, save among the Annulosa. I have hitherto 

 been accustomed to consider them, under the name of the 

 ANNTJLOIDA, as a division of this sub-kingdom ; but until some 

 structural character can be discovered by which all the 

 Annuloida agree with the Annulosa, and differ from other 

 animals, I am much inclined to think it would conduce to the 

 formation of clear conceptions in zoology if the Annuloida 

 were regarded as a distinct primary division of the Animal 

 Kingdom. 



If we now turn to the other column of classes of invertebrate 

 animals (p. 6), the last four on the list, viz., Cephalopoda, 

 Pteropoda, Pulmogasieropoda, and Branehiogasteropoda, have a 

 number of well-marked characters in common. In all, the 

 nervous system is composed of three principal pairs of ganglia 

 cerebral, pedal, and parieto-splanchnic united by commis- 

 sures. All possess that remarkable buccal apparatus, the 

 odontophore, whence I have ventured to propose the name of 

 ODONTOPHORA for the group. The circulatory and respiratory 

 organs vary a great deal, but none are provided with double 

 lamellar gills upon each side of the body. 



The Lamellibranchiata stand in somewhat the same relation 

 to the Odontopliora as the Annelida to the Arthropoda. The 

 Lamellibranchs have the three fundamental pairs of ganglia of 

 the Odontophora, but they possess no trace of the odontophore. 

 Furthermore, they are all provided with bivalve external pallial 

 shells, the valves being right and left in relation to the body. 



G 



