CHAPTER V. 



THE APPEARANCE OF VERTEHRATE ANIMALS. 



CONFESSEDLY the highest style of animal is that which 

 possesses a skull and backbone, with brain and nerve 

 system to match, and which embodies the general plan of 

 structure employed in man himself. Yet among the fishes, 

 which constitute the lowest manifestation of this type, are 

 some so rudimentary that the brain is scarcely developed, and 

 the skeleton is merely a cord of gristle. These are represented 

 in the modern world only by the Lancelot,^ a creature which 

 has sometimes been mistaken for a worm, and by a slightly 

 more advanced type, that of the Lampreys.^ In these 

 animals the Vertebrates make the nearest approach to the 

 lower domains of the animal kingdom, collectively known as 

 Invertebrates. We should naturally expect that since the 

 vertebrates succeed the inferior animals in time, their lower 

 types should appear first, and that these should be aquatic 

 rather than terrestrial. On the other hand, as the oldest fishes 

 that are certainly known are strongly protected with bony 

 armour, and had to contend against formidable Crustaceans and 

 Cuttles, we might suppose that the Lancelot and the Lampreys 

 are rather degraded types belonging to the modern period, than 

 the tme precursors of the other fishes. 



^ Amphioxus. " Petromyzon, etc. 



