THE ANNULOIDA AND ODONTOPIIORA. 79 



described at length the ambulacral system ; and, in speaking of 

 the Scolecida, I have no less insisted upon the peculiarities of 

 the " water-vascular system." But it is impossible to compare 

 these two systems of vessels without being struck by their 

 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 Phyl- 

 lopod Crustacea militates against the homology of these limbs 

 with the purely locomotive appendages of other Crustaceans. 



Thus it appears that the Ecliinodermata and the Scole- 

 eida 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 Annuloida, as a division of this sub-kingdom ; but until 

 some structural character can be discovered by which all the 

 Annuhida agree with the Annidosa, and differ from other 

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

 formation of clear conceptions in zoology if the Annuhida were 

 regarded as a distinct primary division of the Animal Kingdom. 



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

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

 Pteropjoda, Pulmogasteropoda, and Branchiogasteropoda, 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 commissures. 

 All possess that remarkable buccal apparatus, the odontophore, — 

 whence I have ventured to propose the name of Odontophoka 

 for the group. The circulatory and respiratory organs vary a 

 good deal, but none are provided with double lamellar gills upon 

 each side of the body. 



The Lamellibr and data stand in somewhat the same relation 

 to the Odoidophora as the Annelida to the Arthropoda. The 



