VERTEBRATA. 



CHAPTER I. 



CHARACTERS OF VERTEBRATE ANIMALS. ACRANIA. 



~* i. Introductory. The animals which make up the 

 sub-kingdom Vertebrata are the fishes, reptiles, birds, 

 and quadrupeds ; and as they present to us a greater 

 number of interesting points in structure, function, and 

 habits than all the other sub -kingdoms put together, 

 and as they are for the most part of large size and of 

 complex organisation, they require a more careful and 

 detailed study than do the animals which make up the 

 other sub-kingdoms. On this account, Vertebrata, 

 though in reality constituting only a subdivision equi- 

 valent to any of the other sub-kingdoms, such as 

 Mollusca, Polystomata, or Vermes, are yet often treated, 

 and naturally so, as if they equalled all the other sub- 

 kingdoms collectively. 



2. General characters of vertebrate animals. 

 Every vertebrate animal possesses in the centre of 

 its body an axis or rod of cartilage, which forms a 

 B 



