REVIEWS — PRINCIPLES OF ORGANIC ARCHITECTURE. 281 



ent models and the Protozoa represent the lowest degree of develop- 

 ment consistent with animal life. The following introductory account 

 of the points of agreement and difference between Vertebrata and 

 Articulata is deserving of attention : " In the following remarks 

 attention will be directed mainly, and in the first place to the Articu- 

 late and Vertebrate groups, which appear to form a natural series 

 distinguished by some remarkable peculiarities, wanting in the other 

 two [Mollusca and Radiata], especially by the presence of a jointed 

 frame-work or skeleton, for the support of the soft parts of the body. 

 This is a character indicated by their names, Vertebrata and Articu- 

 lata, meaning respectively, hinged and jointed animals, and suggest- 

 ing the same general idea of a series of parts, so connected as to 

 turn on each other, in the manner of a hinge or joint. All these 

 animals, in fact, have in so far the same general conformation, that 

 their skeleton consists of a series of pieces, placed one in front of 

 the other, so as to form an elongated shaft, which, notwithstanding 

 the rigid nature of the several parts, has a certain flexibility, owing 

 to the numerous joints connecting these together. At the anterior 

 end of this column is the head, in which, along with the principal 

 organs of sense, is situated the mouth or anterior opening of the 

 alimentary canal, closed by movable jaws. The animal is also furnished 

 with locomotive organs or limbs, all having a downward direction, 

 and jointed like the shaft of the skeleton, to which they are connected 

 in pairs. The arrangement of these parts, and indeed the whole 

 organisation of the animal, is highly symmetrical in its earliest condi- 

 tion, although in many cases, as the embryo assumes the characters 

 of the adult, this is interfered with by the disproportionate develop- 

 ment of certain organs of the body. 



" Bnt Vertebrate and Articulate animals agree farther in some re- 

 spects which do not seem to have any necessary dependence on this 

 segmentation implied in their respective names. In both groups the 

 central tract of the nervous system forms a cord along the axis of 

 the animal, with its anterior extremity developed into an organ having 

 a certain analogy to the human brain. In both the central organs for 

 the circulation of the blood are a contractile vessel or heart, propelling 

 the blood towards the head, and an arterial trunk returning the main 

 current in the opposite direction. In both the digestive system is re- 

 presented by a canal running in the length of the interior of the body, 

 and opening before and behind by appropriate orifices on the lower as- 



