I. SUBKINGDOM VEKTEBRATA: 



General 



tebrates are usually distinguished by a 

 chain of small bones (vertebrae) to which 

 the other parts of the skeleton are at 

 tached.* Certain modifications in the 

 structure of these animals separate them 

 into Classes, according to the following 

 table: 



SUBKINGDOM. 



... , SUCKLE THEIR YOUNG ; LUNGS ; -, 



Viviparous RESPIRATION SIMPLE; BLOOD 



(producing \ WARM ; CIRCULATION DOUBLE 



1Vlng . AND COMPLETE ; HEART FOUR- 



t CHAMBERED. 



(birds}. 



Vertebral Column. 



RESPIRATION 

 AQUATIC, WITH 



GILLS. 



f Blood cold ; ] 

 J. heart mostly i- 

 [ two-chambered. J 



Amphibia, 



Pisces 

 (fishes). 



* For a description of the vertebral column, and the advantages of its peculiar 

 form, see "Fourteen Weeks in Physk.logy," page 27, et seq. 



