THE CLASSIFICATION OF THE VERTEBKATA, 181 



generality of zoologists that a structure like the tunicate 

 notochorcl, present in the larva and liable afterwards to 

 chsappear, conforms rather to the characters of a vestigial 

 than of a new structure, so that the evidence favours the 

 speculation that the Tunicates are degenerate Verteb rata rather 

 than precursors of that highest primary division of animals. 

 But what I wrote still remains true, and we are in the position 

 that if we believe that the Vertebrata proceeded from an 

 invertebrate form, the only hypothesis which seems in 

 harmony with the evidence is, that the invertebrate ancestor 

 was devoid of a ventral chain of ganglia, and had a supra- 

 oesophageal ganglion of which our whole cerebro- spinal axis 

 is the grand evolution. This being the case it is plain that 

 there is much to be said in favour of the name given on 

 Okenite principles by Cams to the Vertebrata, namely, 

 "Cephalozoaries ; but even more is to be said in favour of the 

 appreciations of Lamarck when he divided animals into 

 two grand divisions, ^az., Vertebrata and Invertebrata. For 

 the whole scope of the animal kingdom is the evolution of 

 ■consciousness and of volition, and it is not till the Vertebrata 

 are reached that the organ of consciousness subordinates to 

 it the whole body, and particularly the animal sphere. 



A word may be added here with reference to the limbs of 

 the Vertebrata. They are in certain instances suppressed 

 altogether, and in other instances there is only one pair of 

 them developed, but nevertheless no one Avill cavil at its being 

 considered a characteristic of all the main divisions, from 

 fishes to mammals, that they have two pairs of limbs, always 

 homologous. It is true that there is a plausible theory 

 current among biologists as to the origin of the limbs, that 

 they are remains of two lateral fins which in some ancestor 

 ran the whole length of the body, and were comparable v/ith 

 the mesial fins still existing in fishes. But we may remark 

 first, that there is no evidence of any weight in favour of 

 this theory ; it is a Dens ex machina. Secondly, there is 

 no explanation offered as to how it came about that it is 

 always the same fore and hind limbs which make their 

 appearance as the evolutions of the assumed lateral fiu, and 

 thirdly, the former existence of such a continuous fin, in the 

 days when the assumed forms, bridging the gap between 

 Invertebrates and Vertebrates, were the highest as yet 

 brought into being, does not interfere with the importance 

 of the two pairs of limbs as a characteristic vertebrate featm-e. 



We now come to the classification of Vertebrata, and 



