REVIEWS — PRINCIPLES OF ORGANIC ARCHITECTURE. 283 



" 2. la the Ventral or lower surface (on which are situated the limbs and 

 the two orifices of the Alimentary caoal) coinciding in Vertebi-ata 

 with the haemal aspect. 

 In Articulata, with the neural aspect. 

 " 3. In the anterior end of the Alimentary canal, reaching this surface by 

 traversing: — 

 In Yertebrata a vascular loop ; 

 In Articulata [both a vascular and*] a nervous loop. 

 " 4. In the posterior end of the Alimentary canal, reaching the same sur- 

 face : — 

 In Vertebrata, short of the neuro-vascular spine, which is prolonged 



as a tail ; 

 In Articulata, beyond the termination of the nervous cord, and at 

 the extremity of the body, so that there is no true tail." 



In wbat lie says of the Mollusca, Dr. Ogilvie follows the views of 

 Huxley, a very learned and ingenious man, an original observer, and 

 a bold speculator, who has, we have no doubt, thrown much valuable 

 light on the MoUuscan structure ; but the summary given by our 

 author leaves the difficulties respecting the classes in this sub-king- 

 dom untouched, not even naming several important groups, whose 

 leading characteristics would be interesting to the most general stu- 

 dent. We must refer to the volume itself for the summary of Mr. 

 Huxley's doctrines. Our author remarks upon them that, " though 

 there may attach a certain ambiguity — as he admits himself — to some 

 of his conclusions, he seems to have abundantly established the gene- 

 ral principle that the modifications of the common plan, — which, in 

 Vertebrata and Articulata, are dependent on the over-development or 

 abortion of some of the parts entering into the composition of the 

 several segments, or by the addition or subtraction of entire segments 

 of the skeleton, are to be ascribed in Mollusca to local expansions of 

 certain parts of the soft body of the animal. By such out-growths of 

 particular regions we are to explain not only the very general loss of 

 symmetry, and the neural and haemal flexures characterising the seve- 

 ral classes, but also the origin of such appendages as the arms and 

 funnel of the cuttle-fish, and the gill tufts and tentacles of other 

 Mollusca. Even the so-called external skeleton or shell — which is 

 certainly the most permanent, as it is to general observers the most 

 characteristic feature of the group — is merely the calcareous cast of 

 such an expansion, being moulded on the fold termed the mantle, 



The bracketed words apply only to a portion of Articulata. 



