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the functions of Organic, as distinguished from Animal Life, the Mollusca are 

 nearer Fishes, the lowest class of Yertebrata, than are the Articulata. In 

 continuously tracing the upward course of Nature, we must, therefore, come 

 down again, as it were, from the topmost Articulata in order to regain the 

 main line of progressive development. 



Pursuing this course, we revert to the highest of the Mollusca, the 

 Cephalopoda ; and here we find the first hint of the structure which gives to 

 Animals of the highest Sub-Kingdom the name of Vertebrata. The Nervous 

 centres of the Insect aie protected by firmly jointed rings, which may be 

 regarded as an exterior skeleton. But the Cephalopod, known as the Cuttle- 

 fish, possesses in the bone, which is a well-known article of commerce, the 

 rudiments of a true internal skeleton. If amongst the Articulata we find the 

 first trace of the Spinal Cord, it is here that the bony case which is to hold it 

 begins to make its appearance. 



You are of course aware that the Spinal Column, or backbone in Man 

 and all Vertebrated Animals, consists of a series of bones strongly connected 

 together, called Vertebrae. Now the received doctrine of modern osteologists 

 is, that the whole skeleton is derived from the development of the elements of 

 Vertebrae. The Human skull is found to be but a continuation of the back- 

 bone, consisting of four developed Vertebrae. The ribs, and even the limbs, 

 are equally developments of vertebral appendages. Now, what is the signifi- 

 cance of this new rigid element in the structure of animals of the highest Sub- 

 Kingdom 1 If we see a man providing himself with a strong box, we judge 

 that he is getting ready a safe receptacle for treasure ; and similarly this new 

 precaution taken by Nature in the structure of the Spinal Column and skull 

 surely indicates that the contents of these parts are of paramount importance 

 in the animal economy — as we know to be the case. 



The Vertebrata are divided into four great classes — I. Mammalia (Qucklevs) ; 

 H. Aves (Birds) ; III. Reptilia (Reptiles) ; IV. Pisces (Fishes). The gradual 

 ascent in type is even more evident in this division of the Animal Kingdom 

 than in the lower part of the scale. This diagram shows how the three 

 superior classes of Mammals, Birds, and Reptiles, rise gradually upwards, 

 each above the one immediately below it, by the improvement of some vital 

 function ; each advance implying increased organic complexity and fitting the 

 creature for a higher mode of life. 



MAMMALS. 



Air-breathing, Warm-blooded, Viviparous. 

 BIEDS. 



Oviparous, Air-breathing, Warm-blooded. 

 REPTILES. 



Cold-blooded, Oviparous, Air-breathing. 

 FISHES. 



Water-breathing, Cold-blooded, Oviparous. 

 The functions which I have here selected for comparison are, you see, all 

 functions of the organic life ; respiration, circulation, and re-production. But 

 I do not mean to abandon that which I have selected as the best criterion of 

 progress in the scale of being, viz., the advancing perfection of the nervous 

 system. The four classes of vertebrates will retain the same relative positions, 

 whether we take as our criterion the perfection of the apparatus of Organic, 

 or that of Animal Life : for the type of Organic Life is raised and improved 

 concurrently with the advance of the Animal Life which it subserves. I have 

 referred to the provision made by Nature in the spinal column and skull for 



