284 REVIEWS — PRINCIPLES OF ORGANIC ARCHITECTURE. 



whose characters it faithfully preserves, even to the papillary pro- 

 longations of its margin, which are a distinguishing mark of some 

 species." 



We think it will probably be decided that the method in most 

 general use of characterising the classes of moUusca in a great degree 

 by their organs of motion is unsatisfactory, and that the groups 

 known as Pteropoda, Heteropoda, and Gasteropoda ought to be 

 combined, the first mentioned being but a less developed state, re- 

 sembling the fry of many G-asteropoda, and the second small group a 

 mere modification of the same general structure. Thus the Cephalous 

 Mollusca, exhibiting the greatest power and activity of which the 

 type admits, would form two classes, the Cephalopoda standing high- 

 est. The Bryozoa display the lowest degree of development in the 

 whole sub-kingdom ; Tunicafa will stand next ; and Conchifera, unit- 

 ing the Lamellibranchiate and Palliobranchiate groups, which are but 

 sub-classes, will complete the series, giving us representatives in this 

 sub-kingdom of all the great divisions of the animal kingdom, in 

 classes which, both as to the essential agreement of their members 

 and the soundness of the distinctions employed, are as good as we 

 can find in any part of the system. 



As we descend in the scale of being we find the number of the 

 greater divisions diminished, and the characters less easily appreci- 

 able. In our opinion the sub-kingdom Eadiata is sufiiciently bound 

 together by its characteristic arrangement of its nervous system and 

 its striking external character ; and we are equally satisfied that its 

 three classes Echinodermata, Acalephae, and Polypifera, ought to be 

 distinguished. Cuvier combined the two former under the name of 

 Radiaria, whilst filling up the sub-kingdom with lower developments 

 of other types, in which either no perceptible nervous system, or a 

 very rudimentary one, could be found. Mr. Huxley, in a more 

 advanced stage of knowledge on the subject, rightly perceives the 

 Acalephae to be rather connected in all important points of structure 

 with Polypifera ; but, acknowledging the justness of his views thus 

 far, we are not prepared to run these two classes into one, or to sepa- 

 rate them altogether from Echinodermata, which latter, notwith- 

 standing certain analogies which mark their higher position, must, in 

 our opinion, be excluded from Articulata. The attempt to do away 

 with the distinctness of the Radiate type does, at present, we must con- 

 fess, look to us like straining after novelty at the expense of nature and 



