CHAPTER II 



PHYSIOLOGICAL CLASSIFICATION 



THE animal kingdom, according to the teaching 

 which was customary in Professor Huxley's time, 

 was arranged under the two great divisions of 

 the vertebrata or animals provided with a jointed 

 axial skeleton, the backbone, and the invertebrata 

 or animals destitute of a backbone ; whereby a 

 single phylum or primary branch of the tree of 

 life was contrasted and placed upon an apparent 

 equality with a whole complex of other phyla. 

 This method of classification denoted one of 

 the great generalisations in zoology at the birth 

 of the nineteenth century, enduring from the 

 beginning to the end of that century. Those 

 who attend to these matters no longer continue 

 to oppose the homogeneous group of the verte- 

 brates to the negative association of invertebrates. 

 The former term, introduced by Lamarck and 

 Cuvier, retains its full significance, but the word 

 invertebrate, though still useful as an adjective, 

 is comparatively barren as an idea. 



The classification now adopted is one based 

 13 



